Finding the angle of a complex fraction
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If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
For example, my textbook says that for the fraction $$z=frac{jomega}{1+jomega},$$ the phase angle should be $$arctan(frac{1}{omega}).$$ I'm not really understanding what method/identities they're using to arrive at this answer.Is there a standard way to find the phase angle of a complex fraction?
trigonometry complex-numbers
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add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
For example, my textbook says that for the fraction $$z=frac{jomega}{1+jomega},$$ the phase angle should be $$arctan(frac{1}{omega}).$$ I'm not really understanding what method/identities they're using to arrive at this answer.Is there a standard way to find the phase angle of a complex fraction?
trigonometry complex-numbers
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$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25
add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
For example, my textbook says that for the fraction $$z=frac{jomega}{1+jomega},$$ the phase angle should be $$arctan(frac{1}{omega}).$$ I'm not really understanding what method/identities they're using to arrive at this answer.Is there a standard way to find the phase angle of a complex fraction?
trigonometry complex-numbers
$endgroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
For example, my textbook says that for the fraction $$z=frac{jomega}{1+jomega},$$ the phase angle should be $$arctan(frac{1}{omega}).$$ I'm not really understanding what method/identities they're using to arrive at this answer.Is there a standard way to find the phase angle of a complex fraction?
trigonometry complex-numbers
trigonometry complex-numbers
asked Oct 19 '15 at 16:17
nichinichi
1313
1313
$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25
add a comment |
$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25
$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25
$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
If $z = a+bj$ where $a$ and $b$ are real, then you can determine the phase angle as $arctanleft(frac{b}{a}right)$ (as long as you are careful about the signs and quadrants), since $a+bj$ represents a point in the complex plane, and the phase angle is the angle this vector makes with the $x$-axis. So for the example from your textbook,
begin{align*}
frac{jomega}{1+jomega} = frac{jomega(1-jomega)}{(1+jomega)(1-jomega)}
= frac{omega^2 + jomega}{1+omega^2}.
end{align*}
Then the phase angle is $arctanleft(frac{omega}{omega^2}right) = arctanleft(frac{1}{omega}right)$, as the book says.
If you take the fraction you are given, $frac{a+bi}{c+di}$ and rationalize the denominator, you should be able to write the phase angle as an arctangent just as above.
$endgroup$
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
add a comment |
$begingroup$
The argument of the complex number $frac{a+bi}{c+di}$ is just the difference between the arguments of $a+bi$ and $c+di$.
So you really just need to know how to compute the argument of any complex number $a+bi$ (and then you simply compute a difference of two arguments).
- If $a > 0$, this is indeed $arctan left(frac{b}{a}right)$.
- If $a < 0$, this is $arctan left(frac{b}{a}right) pmpi$ depending on the sign of $b$ (I suggest you draw it to see).
- If $a = 0$, this is $pm frac{pi}{2}$ depending depending on the sign of $b$.
$endgroup$
add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
Yes, you can. In fact, I can show you that find phasor angle of the rationalized $z$ is the same as the phasor angle of the numerator minus that of the denominator.
First the rationalization approach:
$$angle frac{a+bi}{c+di} = angle frac{(a+bi)(c-di)}{(c+di)(c-di)} = anglefrac{(ac+bd)+(bc-ad)i}{c^2+d^2} = arctan(frac{bc-ad}{ac+bd})$$
Now calculate the numerator and denominator separately and use Sum of Arctangents: $$arctan a + arctan b = arctan dfrac {a + b} {1 - a b}$$
$$angle(a+bi)-angle(c+di) = arctan(frac{b}{a})-arctan(frac{d}{c}) = arctan(frac{frac{b}{a}-frac{d}{c}}{1+frac{bd}{ac}})=arctan(frac{bc-ad}{ac+bd})$$
$endgroup$
add a comment |
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3 Answers
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active
oldest
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3 Answers
3
active
oldest
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$begingroup$
If $z = a+bj$ where $a$ and $b$ are real, then you can determine the phase angle as $arctanleft(frac{b}{a}right)$ (as long as you are careful about the signs and quadrants), since $a+bj$ represents a point in the complex plane, and the phase angle is the angle this vector makes with the $x$-axis. So for the example from your textbook,
begin{align*}
frac{jomega}{1+jomega} = frac{jomega(1-jomega)}{(1+jomega)(1-jomega)}
= frac{omega^2 + jomega}{1+omega^2}.
end{align*}
Then the phase angle is $arctanleft(frac{omega}{omega^2}right) = arctanleft(frac{1}{omega}right)$, as the book says.
If you take the fraction you are given, $frac{a+bi}{c+di}$ and rationalize the denominator, you should be able to write the phase angle as an arctangent just as above.
$endgroup$
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
add a comment |
$begingroup$
If $z = a+bj$ where $a$ and $b$ are real, then you can determine the phase angle as $arctanleft(frac{b}{a}right)$ (as long as you are careful about the signs and quadrants), since $a+bj$ represents a point in the complex plane, and the phase angle is the angle this vector makes with the $x$-axis. So for the example from your textbook,
begin{align*}
frac{jomega}{1+jomega} = frac{jomega(1-jomega)}{(1+jomega)(1-jomega)}
= frac{omega^2 + jomega}{1+omega^2}.
end{align*}
Then the phase angle is $arctanleft(frac{omega}{omega^2}right) = arctanleft(frac{1}{omega}right)$, as the book says.
If you take the fraction you are given, $frac{a+bi}{c+di}$ and rationalize the denominator, you should be able to write the phase angle as an arctangent just as above.
$endgroup$
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
add a comment |
$begingroup$
If $z = a+bj$ where $a$ and $b$ are real, then you can determine the phase angle as $arctanleft(frac{b}{a}right)$ (as long as you are careful about the signs and quadrants), since $a+bj$ represents a point in the complex plane, and the phase angle is the angle this vector makes with the $x$-axis. So for the example from your textbook,
begin{align*}
frac{jomega}{1+jomega} = frac{jomega(1-jomega)}{(1+jomega)(1-jomega)}
= frac{omega^2 + jomega}{1+omega^2}.
end{align*}
Then the phase angle is $arctanleft(frac{omega}{omega^2}right) = arctanleft(frac{1}{omega}right)$, as the book says.
If you take the fraction you are given, $frac{a+bi}{c+di}$ and rationalize the denominator, you should be able to write the phase angle as an arctangent just as above.
$endgroup$
If $z = a+bj$ where $a$ and $b$ are real, then you can determine the phase angle as $arctanleft(frac{b}{a}right)$ (as long as you are careful about the signs and quadrants), since $a+bj$ represents a point in the complex plane, and the phase angle is the angle this vector makes with the $x$-axis. So for the example from your textbook,
begin{align*}
frac{jomega}{1+jomega} = frac{jomega(1-jomega)}{(1+jomega)(1-jomega)}
= frac{omega^2 + jomega}{1+omega^2}.
end{align*}
Then the phase angle is $arctanleft(frac{omega}{omega^2}right) = arctanleft(frac{1}{omega}right)$, as the book says.
If you take the fraction you are given, $frac{a+bi}{c+di}$ and rationalize the denominator, you should be able to write the phase angle as an arctangent just as above.
answered Oct 19 '15 at 16:27
rogerlrogerl
18k22747
18k22747
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
add a comment |
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
$begingroup$
Thank you very much! This is the answer I was looking for. The book didn't go into much depth into how to find the phase angle for fractions, so I had to try to understand what they were saying.
$endgroup$
– nichi
Oct 19 '15 at 16:38
add a comment |
$begingroup$
The argument of the complex number $frac{a+bi}{c+di}$ is just the difference between the arguments of $a+bi$ and $c+di$.
So you really just need to know how to compute the argument of any complex number $a+bi$ (and then you simply compute a difference of two arguments).
- If $a > 0$, this is indeed $arctan left(frac{b}{a}right)$.
- If $a < 0$, this is $arctan left(frac{b}{a}right) pmpi$ depending on the sign of $b$ (I suggest you draw it to see).
- If $a = 0$, this is $pm frac{pi}{2}$ depending depending on the sign of $b$.
$endgroup$
add a comment |
$begingroup$
The argument of the complex number $frac{a+bi}{c+di}$ is just the difference between the arguments of $a+bi$ and $c+di$.
So you really just need to know how to compute the argument of any complex number $a+bi$ (and then you simply compute a difference of two arguments).
- If $a > 0$, this is indeed $arctan left(frac{b}{a}right)$.
- If $a < 0$, this is $arctan left(frac{b}{a}right) pmpi$ depending on the sign of $b$ (I suggest you draw it to see).
- If $a = 0$, this is $pm frac{pi}{2}$ depending depending on the sign of $b$.
$endgroup$
add a comment |
$begingroup$
The argument of the complex number $frac{a+bi}{c+di}$ is just the difference between the arguments of $a+bi$ and $c+di$.
So you really just need to know how to compute the argument of any complex number $a+bi$ (and then you simply compute a difference of two arguments).
- If $a > 0$, this is indeed $arctan left(frac{b}{a}right)$.
- If $a < 0$, this is $arctan left(frac{b}{a}right) pmpi$ depending on the sign of $b$ (I suggest you draw it to see).
- If $a = 0$, this is $pm frac{pi}{2}$ depending depending on the sign of $b$.
$endgroup$
The argument of the complex number $frac{a+bi}{c+di}$ is just the difference between the arguments of $a+bi$ and $c+di$.
So you really just need to know how to compute the argument of any complex number $a+bi$ (and then you simply compute a difference of two arguments).
- If $a > 0$, this is indeed $arctan left(frac{b}{a}right)$.
- If $a < 0$, this is $arctan left(frac{b}{a}right) pmpi$ depending on the sign of $b$ (I suggest you draw it to see).
- If $a = 0$, this is $pm frac{pi}{2}$ depending depending on the sign of $b$.
answered Oct 19 '15 at 16:33
Joel CohenJoel Cohen
7,33412137
7,33412137
add a comment |
add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
Yes, you can. In fact, I can show you that find phasor angle of the rationalized $z$ is the same as the phasor angle of the numerator minus that of the denominator.
First the rationalization approach:
$$angle frac{a+bi}{c+di} = angle frac{(a+bi)(c-di)}{(c+di)(c-di)} = anglefrac{(ac+bd)+(bc-ad)i}{c^2+d^2} = arctan(frac{bc-ad}{ac+bd})$$
Now calculate the numerator and denominator separately and use Sum of Arctangents: $$arctan a + arctan b = arctan dfrac {a + b} {1 - a b}$$
$$angle(a+bi)-angle(c+di) = arctan(frac{b}{a})-arctan(frac{d}{c}) = arctan(frac{frac{b}{a}-frac{d}{c}}{1+frac{bd}{ac}})=arctan(frac{bc-ad}{ac+bd})$$
$endgroup$
add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
Yes, you can. In fact, I can show you that find phasor angle of the rationalized $z$ is the same as the phasor angle of the numerator minus that of the denominator.
First the rationalization approach:
$$angle frac{a+bi}{c+di} = angle frac{(a+bi)(c-di)}{(c+di)(c-di)} = anglefrac{(ac+bd)+(bc-ad)i}{c^2+d^2} = arctan(frac{bc-ad}{ac+bd})$$
Now calculate the numerator and denominator separately and use Sum of Arctangents: $$arctan a + arctan b = arctan dfrac {a + b} {1 - a b}$$
$$angle(a+bi)-angle(c+di) = arctan(frac{b}{a})-arctan(frac{d}{c}) = arctan(frac{frac{b}{a}-frac{d}{c}}{1+frac{bd}{ac}})=arctan(frac{bc-ad}{ac+bd})$$
$endgroup$
add a comment |
$begingroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
Yes, you can. In fact, I can show you that find phasor angle of the rationalized $z$ is the same as the phasor angle of the numerator minus that of the denominator.
First the rationalization approach:
$$angle frac{a+bi}{c+di} = angle frac{(a+bi)(c-di)}{(c+di)(c-di)} = anglefrac{(ac+bd)+(bc-ad)i}{c^2+d^2} = arctan(frac{bc-ad}{ac+bd})$$
Now calculate the numerator and denominator separately and use Sum of Arctangents: $$arctan a + arctan b = arctan dfrac {a + b} {1 - a b}$$
$$angle(a+bi)-angle(c+di) = arctan(frac{b}{a})-arctan(frac{d}{c}) = arctan(frac{frac{b}{a}-frac{d}{c}}{1+frac{bd}{ac}})=arctan(frac{bc-ad}{ac+bd})$$
$endgroup$
If I have a complex fraction, say $$z=frac{a+bi}{c+di}$$, how can I find the phase angle of this? Could I just calculate it using $$arctan(frac{b}{a})-arctan(frac{d}{c})?$$
Yes, you can. In fact, I can show you that find phasor angle of the rationalized $z$ is the same as the phasor angle of the numerator minus that of the denominator.
First the rationalization approach:
$$angle frac{a+bi}{c+di} = angle frac{(a+bi)(c-di)}{(c+di)(c-di)} = anglefrac{(ac+bd)+(bc-ad)i}{c^2+d^2} = arctan(frac{bc-ad}{ac+bd})$$
Now calculate the numerator and denominator separately and use Sum of Arctangents: $$arctan a + arctan b = arctan dfrac {a + b} {1 - a b}$$
$$angle(a+bi)-angle(c+di) = arctan(frac{b}{a})-arctan(frac{d}{c}) = arctan(frac{frac{b}{a}-frac{d}{c}}{1+frac{bd}{ac}})=arctan(frac{bc-ad}{ac+bd})$$
answered Dec 21 '18 at 13:41
johanjohan
11
11
add a comment |
add a comment |
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$begingroup$
If $z=frac{z_1}{z_2}$ then $arg(z)=arg(z_1)-arg(z_2)$. It is known.
$endgroup$
– G-man
Oct 19 '15 at 16:25