The integral of $int_{-pi/4}^{pi/4} frac{t^4tan(t)}{2+cos(t)},dt$?
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Here is the definite integral: $$int_{-pi/4}^{pi/4} frac{t^4tan(t)}{2+cos(t)},dt$$
Apparently this evaluates to zero. I don't see any patterns at all and I have no idea how I'd evaluate it. I tried graphing this on desmos and it wasn't pretty; there are asymptotes everywhere. Shouldn't this be undefined because of the asymptotes? Even if it isn't undefined, what would the antiderivative of this possible be?
And most importantly, why does it evaluate to zero, and is there something that should've told me that?
Any help is appreciated.
calculus integration
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add a comment |
$begingroup$
Here is the definite integral: $$int_{-pi/4}^{pi/4} frac{t^4tan(t)}{2+cos(t)},dt$$
Apparently this evaluates to zero. I don't see any patterns at all and I have no idea how I'd evaluate it. I tried graphing this on desmos and it wasn't pretty; there are asymptotes everywhere. Shouldn't this be undefined because of the asymptotes? Even if it isn't undefined, what would the antiderivative of this possible be?
And most importantly, why does it evaluate to zero, and is there something that should've told me that?
Any help is appreciated.
calculus integration
$endgroup$
add a comment |
$begingroup$
Here is the definite integral: $$int_{-pi/4}^{pi/4} frac{t^4tan(t)}{2+cos(t)},dt$$
Apparently this evaluates to zero. I don't see any patterns at all and I have no idea how I'd evaluate it. I tried graphing this on desmos and it wasn't pretty; there are asymptotes everywhere. Shouldn't this be undefined because of the asymptotes? Even if it isn't undefined, what would the antiderivative of this possible be?
And most importantly, why does it evaluate to zero, and is there something that should've told me that?
Any help is appreciated.
calculus integration
$endgroup$
Here is the definite integral: $$int_{-pi/4}^{pi/4} frac{t^4tan(t)}{2+cos(t)},dt$$
Apparently this evaluates to zero. I don't see any patterns at all and I have no idea how I'd evaluate it. I tried graphing this on desmos and it wasn't pretty; there are asymptotes everywhere. Shouldn't this be undefined because of the asymptotes? Even if it isn't undefined, what would the antiderivative of this possible be?
And most importantly, why does it evaluate to zero, and is there something that should've told me that?
Any help is appreciated.
calculus integration
calculus integration
edited Dec 9 '18 at 21:03
Paul Enta
4,72611333
4,72611333
asked Dec 9 '18 at 20:56
James RonaldJames Ronald
1057
1057
add a comment |
add a comment |
4 Answers
4
active
oldest
votes
$begingroup$
You will find that definite integral questions with funky integrands are not generally solvable by the routine method of taking the anti-derivative, as it may be very hard to find.
Note that here, the integrand is an odd function.
$f(t)=frac{t^4tan t}{2+cos t}implies f(-t)=-frac{t^4tan t}{2+cos t}=-f(t)$
Recall that for an odd function $f, int_{-a}^af=0$
As far as asymptotes and discontinuity of $f$ is concerned, note that $f$ is only discontinuous at odd multiples of $pi/2$ and the domain of $t, (-pi/4, +pi/4)$ does not contain any points of discontinuity.
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Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
add a comment |
$begingroup$
Hint:
$$frac{(-t)^4tan(-t)}{2+cos(-t)}=-frac{t^4tan(t)}{2+cos(t)}$$
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Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
add a comment |
$begingroup$
$$I=int_{-a}^{a}frac{t^4tan t}{2+cos t}mathrm dt$$
$t=-u$:
$$I=int_{a}^{-a}frac{(-u)^4tan(-u)}{2+cos(-u)}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4(-tan u)}{2+cos u}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-int_{-a}^{a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-I$$
$$2I=0$$
$$I=0$$
QED
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$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
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@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
add a comment |
$begingroup$
$$int_{-a}^af(t)mathrm dt=0$$
if $f$ is an odd function. That's because odd functions are symmetric w.r.t. the origin, then if $f$ from $0$ to $a$ is defined in the first quadrant (positive area), from $-a$ to $0$ $f$ is defined in the third quadrant (negative area), thus the two areas cancel out.
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$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
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votes
active
oldest
votes
$begingroup$
You will find that definite integral questions with funky integrands are not generally solvable by the routine method of taking the anti-derivative, as it may be very hard to find.
Note that here, the integrand is an odd function.
$f(t)=frac{t^4tan t}{2+cos t}implies f(-t)=-frac{t^4tan t}{2+cos t}=-f(t)$
Recall that for an odd function $f, int_{-a}^af=0$
As far as asymptotes and discontinuity of $f$ is concerned, note that $f$ is only discontinuous at odd multiples of $pi/2$ and the domain of $t, (-pi/4, +pi/4)$ does not contain any points of discontinuity.
$endgroup$
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
add a comment |
$begingroup$
You will find that definite integral questions with funky integrands are not generally solvable by the routine method of taking the anti-derivative, as it may be very hard to find.
Note that here, the integrand is an odd function.
$f(t)=frac{t^4tan t}{2+cos t}implies f(-t)=-frac{t^4tan t}{2+cos t}=-f(t)$
Recall that for an odd function $f, int_{-a}^af=0$
As far as asymptotes and discontinuity of $f$ is concerned, note that $f$ is only discontinuous at odd multiples of $pi/2$ and the domain of $t, (-pi/4, +pi/4)$ does not contain any points of discontinuity.
$endgroup$
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
add a comment |
$begingroup$
You will find that definite integral questions with funky integrands are not generally solvable by the routine method of taking the anti-derivative, as it may be very hard to find.
Note that here, the integrand is an odd function.
$f(t)=frac{t^4tan t}{2+cos t}implies f(-t)=-frac{t^4tan t}{2+cos t}=-f(t)$
Recall that for an odd function $f, int_{-a}^af=0$
As far as asymptotes and discontinuity of $f$ is concerned, note that $f$ is only discontinuous at odd multiples of $pi/2$ and the domain of $t, (-pi/4, +pi/4)$ does not contain any points of discontinuity.
$endgroup$
You will find that definite integral questions with funky integrands are not generally solvable by the routine method of taking the anti-derivative, as it may be very hard to find.
Note that here, the integrand is an odd function.
$f(t)=frac{t^4tan t}{2+cos t}implies f(-t)=-frac{t^4tan t}{2+cos t}=-f(t)$
Recall that for an odd function $f, int_{-a}^af=0$
As far as asymptotes and discontinuity of $f$ is concerned, note that $f$ is only discontinuous at odd multiples of $pi/2$ and the domain of $t, (-pi/4, +pi/4)$ does not contain any points of discontinuity.
edited Dec 10 '18 at 11:00
answered Dec 9 '18 at 20:59
Shubham JohriShubham Johri
5,017717
5,017717
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
add a comment |
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
$begingroup$
Thank you so much! That was a very simply but thorough addressed all my questions, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:44
add a comment |
$begingroup$
Hint:
$$frac{(-t)^4tan(-t)}{2+cos(-t)}=-frac{t^4tan(t)}{2+cos(t)}$$
$endgroup$
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
add a comment |
$begingroup$
Hint:
$$frac{(-t)^4tan(-t)}{2+cos(-t)}=-frac{t^4tan(t)}{2+cos(t)}$$
$endgroup$
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
add a comment |
$begingroup$
Hint:
$$frac{(-t)^4tan(-t)}{2+cos(-t)}=-frac{t^4tan(t)}{2+cos(t)}$$
$endgroup$
Hint:
$$frac{(-t)^4tan(-t)}{2+cos(-t)}=-frac{t^4tan(t)}{2+cos(t)}$$
answered Dec 9 '18 at 21:00
BotondBotond
5,6822732
5,6822732
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
add a comment |
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
Yes I noticed that and now the answer seems very obvious haha, thanks!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
add a comment |
$begingroup$
$$I=int_{-a}^{a}frac{t^4tan t}{2+cos t}mathrm dt$$
$t=-u$:
$$I=int_{a}^{-a}frac{(-u)^4tan(-u)}{2+cos(-u)}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4(-tan u)}{2+cos u}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-int_{-a}^{a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-I$$
$$2I=0$$
$$I=0$$
QED
$endgroup$
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
add a comment |
$begingroup$
$$I=int_{-a}^{a}frac{t^4tan t}{2+cos t}mathrm dt$$
$t=-u$:
$$I=int_{a}^{-a}frac{(-u)^4tan(-u)}{2+cos(-u)}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4(-tan u)}{2+cos u}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-int_{-a}^{a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-I$$
$$2I=0$$
$$I=0$$
QED
$endgroup$
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
add a comment |
$begingroup$
$$I=int_{-a}^{a}frac{t^4tan t}{2+cos t}mathrm dt$$
$t=-u$:
$$I=int_{a}^{-a}frac{(-u)^4tan(-u)}{2+cos(-u)}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4(-tan u)}{2+cos u}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-int_{-a}^{a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-I$$
$$2I=0$$
$$I=0$$
QED
$endgroup$
$$I=int_{-a}^{a}frac{t^4tan t}{2+cos t}mathrm dt$$
$t=-u$:
$$I=int_{a}^{-a}frac{(-u)^4tan(-u)}{2+cos(-u)}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4(-tan u)}{2+cos u}(-mathrm du)$$
$$I=int_{a}^{-a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-int_{-a}^{a}frac{u^4tan u}{2+cos u}mathrm du$$
$$I=-I$$
$$2I=0$$
$$I=0$$
QED
answered Dec 9 '18 at 21:12
clathratusclathratus
3,907334
3,907334
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
add a comment |
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
It's nice to see a straight up proof, didn't know you could do this using the property of even/odd, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:45
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
$begingroup$
@JamesRonald You're very welcome. It's always a good thing to try when you are unsure of how to start on an integral.
$endgroup$
– clathratus
Dec 10 '18 at 20:14
add a comment |
$begingroup$
$$int_{-a}^af(t)mathrm dt=0$$
if $f$ is an odd function. That's because odd functions are symmetric w.r.t. the origin, then if $f$ from $0$ to $a$ is defined in the first quadrant (positive area), from $-a$ to $0$ $f$ is defined in the third quadrant (negative area), thus the two areas cancel out.
$endgroup$
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
add a comment |
$begingroup$
$$int_{-a}^af(t)mathrm dt=0$$
if $f$ is an odd function. That's because odd functions are symmetric w.r.t. the origin, then if $f$ from $0$ to $a$ is defined in the first quadrant (positive area), from $-a$ to $0$ $f$ is defined in the third quadrant (negative area), thus the two areas cancel out.
$endgroup$
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
add a comment |
$begingroup$
$$int_{-a}^af(t)mathrm dt=0$$
if $f$ is an odd function. That's because odd functions are symmetric w.r.t. the origin, then if $f$ from $0$ to $a$ is defined in the first quadrant (positive area), from $-a$ to $0$ $f$ is defined in the third quadrant (negative area), thus the two areas cancel out.
$endgroup$
$$int_{-a}^af(t)mathrm dt=0$$
if $f$ is an odd function. That's because odd functions are symmetric w.r.t. the origin, then if $f$ from $0$ to $a$ is defined in the first quadrant (positive area), from $-a$ to $0$ $f$ is defined in the third quadrant (negative area), thus the two areas cancel out.
answered Dec 9 '18 at 21:29
Lorenzo B.Lorenzo B.
1,8402520
1,8402520
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
add a comment |
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
That definitely makes sense, thank you!
$endgroup$
– James Ronald
Dec 10 '18 at 18:46
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
$begingroup$
You are welcome!
$endgroup$
– Lorenzo B.
Dec 10 '18 at 19:26
add a comment |
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