Solving the integral :$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin2 x}}dx$
$begingroup$
Solving the integral :
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}dx=?$$
My try:
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}cdot frac{1-sqrt{sin 2x}}{1-sqrt{sin 2x}}dx$$
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{1-sin 2x}dx$$
$$(sin x-cos x)^2=1-sin 2x$$
So :
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{(sin x-cos x)^2}dx$$
Now what?
$$$$
calculus integration definite-integrals
$endgroup$
add a comment |
$begingroup$
Solving the integral :
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}dx=?$$
My try:
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}cdot frac{1-sqrt{sin 2x}}{1-sqrt{sin 2x}}dx$$
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{1-sin 2x}dx$$
$$(sin x-cos x)^2=1-sin 2x$$
So :
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{(sin x-cos x)^2}dx$$
Now what?
$$$$
calculus integration definite-integrals
$endgroup$
add a comment |
$begingroup$
Solving the integral :
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}dx=?$$
My try:
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}cdot frac{1-sqrt{sin 2x}}{1-sqrt{sin 2x}}dx$$
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{1-sin 2x}dx$$
$$(sin x-cos x)^2=1-sin 2x$$
So :
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{(sin x-cos x)^2}dx$$
Now what?
$$$$
calculus integration definite-integrals
$endgroup$
Solving the integral :
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}dx=?$$
My try:
$$int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}}cdot frac{1-sqrt{sin 2x}}{1-sqrt{sin 2x}}dx$$
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{1-sin 2x}dx$$
$$(sin x-cos x)^2=1-sin 2x$$
So :
$$int_0^{frac{pi}{2}}frac{sin x(1-sqrt{sin 2x})}{(sin x-cos x)^2}dx$$
Now what?
$$$$
calculus integration definite-integrals
calculus integration definite-integrals
edited Mar 2 at 9:02
Zacky
7,59511061
7,59511061
asked Oct 27 '17 at 19:47
Almot1960Almot1960
2,312824
2,312824
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2 Answers
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$begingroup$
The given integral equals
$$ frac{1}{2}int_{0}^{pi}frac{sintfrac{x}{2}}{1+sqrt{sin x}},dx =frac{1}{2sqrt{2}}int_{0}^{pi}frac{sqrt{1-cos x}}{1+sqrt{sin x}}\=frac{1}{2sqrt{2}}int_{0}^{pi/2}frac{sqrt{1-cos x}+sqrt{1+cos x}}{1+sqrt{sin x}},dx\
=frac{1}{2}int_{0}^{pi/2}frac{sqrt{1+sin x}}{1+sqrt{sin x}},dx$$
or
$$ frac{1}{2}int_{0}^{1}frac{sqrt{1+x}}{sqrt{1-x^2}(1+sqrt{x})},dx = frac{1}{2}int_{0}^{1}frac{dx}{(1+sqrt{x})sqrt{1-x}}=int_{0}^{1}frac{x,dx}{(1+x)sqrt{1-x^2}}$$
which equals $frac{pi}{2}-int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}$. On the other hand
$$ int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}=int_{0}^{pi/2}frac{dtheta}{1+sintheta}=int_{0}^{pi/2}frac{dtheta}{1+costheta}=int_{0}^{pi/2}frac{dtheta}{2cos^2tfrac{theta}{2}}=1, $$
hence:
$$boxed{int_{0}^{pi/2}frac{sin x}{1+sqrt{sin(2x)}},dx = color{blue}{frac{pi}{2}-1},} $$
no particular elliptic integral like $Kleft(frac{1}{2}right)$ or $Eleft(frac{1}{2}right)$ is really involved.
$endgroup$
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
add a comment |
$begingroup$
$$I=int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}},dx$$ Using the fact that: $$int_a^b f(x) dx=frac{1}{2} int_a^b (f(x)+f(a+b-x))dx$$ $$Rightarrow I=frac12 int_0^frac{pi}{2} frac{sin x+cos x}{1+sqrt{sin 2x}}dx$$Now let's substitute $,sin x-cos x=u,$ $rightarrow u^2=1-sin(2x)$$rightarrowsin(2x)=1-u^2$ $$I=int_{0}^{1}frac{du}{1+sqrt{1-u^2}}$$ Letting $u=sin t$ yields: $$I=int_0^{frac{pi}{2}}frac{cos t}{1+cos t},dt= int_0^{frac{pi}{2}}left(frac{1+cos t}{1+cos t}-frac{1}{1+cos t}right),dt$$ $$Rightarrow I=frac{pi}{2}-frac{1}{2}int_0^frac{pi}{2}frac{1}{cos^2frac{t}{2}},dt=frac{pi}{2}-1$$
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
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active
oldest
votes
$begingroup$
The given integral equals
$$ frac{1}{2}int_{0}^{pi}frac{sintfrac{x}{2}}{1+sqrt{sin x}},dx =frac{1}{2sqrt{2}}int_{0}^{pi}frac{sqrt{1-cos x}}{1+sqrt{sin x}}\=frac{1}{2sqrt{2}}int_{0}^{pi/2}frac{sqrt{1-cos x}+sqrt{1+cos x}}{1+sqrt{sin x}},dx\
=frac{1}{2}int_{0}^{pi/2}frac{sqrt{1+sin x}}{1+sqrt{sin x}},dx$$
or
$$ frac{1}{2}int_{0}^{1}frac{sqrt{1+x}}{sqrt{1-x^2}(1+sqrt{x})},dx = frac{1}{2}int_{0}^{1}frac{dx}{(1+sqrt{x})sqrt{1-x}}=int_{0}^{1}frac{x,dx}{(1+x)sqrt{1-x^2}}$$
which equals $frac{pi}{2}-int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}$. On the other hand
$$ int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}=int_{0}^{pi/2}frac{dtheta}{1+sintheta}=int_{0}^{pi/2}frac{dtheta}{1+costheta}=int_{0}^{pi/2}frac{dtheta}{2cos^2tfrac{theta}{2}}=1, $$
hence:
$$boxed{int_{0}^{pi/2}frac{sin x}{1+sqrt{sin(2x)}},dx = color{blue}{frac{pi}{2}-1},} $$
no particular elliptic integral like $Kleft(frac{1}{2}right)$ or $Eleft(frac{1}{2}right)$ is really involved.
$endgroup$
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
add a comment |
$begingroup$
The given integral equals
$$ frac{1}{2}int_{0}^{pi}frac{sintfrac{x}{2}}{1+sqrt{sin x}},dx =frac{1}{2sqrt{2}}int_{0}^{pi}frac{sqrt{1-cos x}}{1+sqrt{sin x}}\=frac{1}{2sqrt{2}}int_{0}^{pi/2}frac{sqrt{1-cos x}+sqrt{1+cos x}}{1+sqrt{sin x}},dx\
=frac{1}{2}int_{0}^{pi/2}frac{sqrt{1+sin x}}{1+sqrt{sin x}},dx$$
or
$$ frac{1}{2}int_{0}^{1}frac{sqrt{1+x}}{sqrt{1-x^2}(1+sqrt{x})},dx = frac{1}{2}int_{0}^{1}frac{dx}{(1+sqrt{x})sqrt{1-x}}=int_{0}^{1}frac{x,dx}{(1+x)sqrt{1-x^2}}$$
which equals $frac{pi}{2}-int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}$. On the other hand
$$ int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}=int_{0}^{pi/2}frac{dtheta}{1+sintheta}=int_{0}^{pi/2}frac{dtheta}{1+costheta}=int_{0}^{pi/2}frac{dtheta}{2cos^2tfrac{theta}{2}}=1, $$
hence:
$$boxed{int_{0}^{pi/2}frac{sin x}{1+sqrt{sin(2x)}},dx = color{blue}{frac{pi}{2}-1},} $$
no particular elliptic integral like $Kleft(frac{1}{2}right)$ or $Eleft(frac{1}{2}right)$ is really involved.
$endgroup$
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
add a comment |
$begingroup$
The given integral equals
$$ frac{1}{2}int_{0}^{pi}frac{sintfrac{x}{2}}{1+sqrt{sin x}},dx =frac{1}{2sqrt{2}}int_{0}^{pi}frac{sqrt{1-cos x}}{1+sqrt{sin x}}\=frac{1}{2sqrt{2}}int_{0}^{pi/2}frac{sqrt{1-cos x}+sqrt{1+cos x}}{1+sqrt{sin x}},dx\
=frac{1}{2}int_{0}^{pi/2}frac{sqrt{1+sin x}}{1+sqrt{sin x}},dx$$
or
$$ frac{1}{2}int_{0}^{1}frac{sqrt{1+x}}{sqrt{1-x^2}(1+sqrt{x})},dx = frac{1}{2}int_{0}^{1}frac{dx}{(1+sqrt{x})sqrt{1-x}}=int_{0}^{1}frac{x,dx}{(1+x)sqrt{1-x^2}}$$
which equals $frac{pi}{2}-int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}$. On the other hand
$$ int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}=int_{0}^{pi/2}frac{dtheta}{1+sintheta}=int_{0}^{pi/2}frac{dtheta}{1+costheta}=int_{0}^{pi/2}frac{dtheta}{2cos^2tfrac{theta}{2}}=1, $$
hence:
$$boxed{int_{0}^{pi/2}frac{sin x}{1+sqrt{sin(2x)}},dx = color{blue}{frac{pi}{2}-1},} $$
no particular elliptic integral like $Kleft(frac{1}{2}right)$ or $Eleft(frac{1}{2}right)$ is really involved.
$endgroup$
The given integral equals
$$ frac{1}{2}int_{0}^{pi}frac{sintfrac{x}{2}}{1+sqrt{sin x}},dx =frac{1}{2sqrt{2}}int_{0}^{pi}frac{sqrt{1-cos x}}{1+sqrt{sin x}}\=frac{1}{2sqrt{2}}int_{0}^{pi/2}frac{sqrt{1-cos x}+sqrt{1+cos x}}{1+sqrt{sin x}},dx\
=frac{1}{2}int_{0}^{pi/2}frac{sqrt{1+sin x}}{1+sqrt{sin x}},dx$$
or
$$ frac{1}{2}int_{0}^{1}frac{sqrt{1+x}}{sqrt{1-x^2}(1+sqrt{x})},dx = frac{1}{2}int_{0}^{1}frac{dx}{(1+sqrt{x})sqrt{1-x}}=int_{0}^{1}frac{x,dx}{(1+x)sqrt{1-x^2}}$$
which equals $frac{pi}{2}-int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}$. On the other hand
$$ int_{0}^{1}frac{dx}{(1+x)sqrt{1-x^2}}=int_{0}^{pi/2}frac{dtheta}{1+sintheta}=int_{0}^{pi/2}frac{dtheta}{1+costheta}=int_{0}^{pi/2}frac{dtheta}{2cos^2tfrac{theta}{2}}=1, $$
hence:
$$boxed{int_{0}^{pi/2}frac{sin x}{1+sqrt{sin(2x)}},dx = color{blue}{frac{pi}{2}-1},} $$
no particular elliptic integral like $Kleft(frac{1}{2}right)$ or $Eleft(frac{1}{2}right)$ is really involved.
answered Oct 27 '17 at 21:39
Jack D'AurizioJack D'Aurizio
291k33284666
291k33284666
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
add a comment |
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
$begingroup$
Nice answer! (y)
$endgroup$
– Darío A. Gutiérrez
Oct 28 '17 at 18:00
add a comment |
$begingroup$
$$I=int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}},dx$$ Using the fact that: $$int_a^b f(x) dx=frac{1}{2} int_a^b (f(x)+f(a+b-x))dx$$ $$Rightarrow I=frac12 int_0^frac{pi}{2} frac{sin x+cos x}{1+sqrt{sin 2x}}dx$$Now let's substitute $,sin x-cos x=u,$ $rightarrow u^2=1-sin(2x)$$rightarrowsin(2x)=1-u^2$ $$I=int_{0}^{1}frac{du}{1+sqrt{1-u^2}}$$ Letting $u=sin t$ yields: $$I=int_0^{frac{pi}{2}}frac{cos t}{1+cos t},dt= int_0^{frac{pi}{2}}left(frac{1+cos t}{1+cos t}-frac{1}{1+cos t}right),dt$$ $$Rightarrow I=frac{pi}{2}-frac{1}{2}int_0^frac{pi}{2}frac{1}{cos^2frac{t}{2}},dt=frac{pi}{2}-1$$
$endgroup$
add a comment |
$begingroup$
$$I=int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}},dx$$ Using the fact that: $$int_a^b f(x) dx=frac{1}{2} int_a^b (f(x)+f(a+b-x))dx$$ $$Rightarrow I=frac12 int_0^frac{pi}{2} frac{sin x+cos x}{1+sqrt{sin 2x}}dx$$Now let's substitute $,sin x-cos x=u,$ $rightarrow u^2=1-sin(2x)$$rightarrowsin(2x)=1-u^2$ $$I=int_{0}^{1}frac{du}{1+sqrt{1-u^2}}$$ Letting $u=sin t$ yields: $$I=int_0^{frac{pi}{2}}frac{cos t}{1+cos t},dt= int_0^{frac{pi}{2}}left(frac{1+cos t}{1+cos t}-frac{1}{1+cos t}right),dt$$ $$Rightarrow I=frac{pi}{2}-frac{1}{2}int_0^frac{pi}{2}frac{1}{cos^2frac{t}{2}},dt=frac{pi}{2}-1$$
$endgroup$
add a comment |
$begingroup$
$$I=int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}},dx$$ Using the fact that: $$int_a^b f(x) dx=frac{1}{2} int_a^b (f(x)+f(a+b-x))dx$$ $$Rightarrow I=frac12 int_0^frac{pi}{2} frac{sin x+cos x}{1+sqrt{sin 2x}}dx$$Now let's substitute $,sin x-cos x=u,$ $rightarrow u^2=1-sin(2x)$$rightarrowsin(2x)=1-u^2$ $$I=int_{0}^{1}frac{du}{1+sqrt{1-u^2}}$$ Letting $u=sin t$ yields: $$I=int_0^{frac{pi}{2}}frac{cos t}{1+cos t},dt= int_0^{frac{pi}{2}}left(frac{1+cos t}{1+cos t}-frac{1}{1+cos t}right),dt$$ $$Rightarrow I=frac{pi}{2}-frac{1}{2}int_0^frac{pi}{2}frac{1}{cos^2frac{t}{2}},dt=frac{pi}{2}-1$$
$endgroup$
$$I=int_0^{frac{pi}{2}}frac{sin x}{1+sqrt{sin 2x}},dx$$ Using the fact that: $$int_a^b f(x) dx=frac{1}{2} int_a^b (f(x)+f(a+b-x))dx$$ $$Rightarrow I=frac12 int_0^frac{pi}{2} frac{sin x+cos x}{1+sqrt{sin 2x}}dx$$Now let's substitute $,sin x-cos x=u,$ $rightarrow u^2=1-sin(2x)$$rightarrowsin(2x)=1-u^2$ $$I=int_{0}^{1}frac{du}{1+sqrt{1-u^2}}$$ Letting $u=sin t$ yields: $$I=int_0^{frac{pi}{2}}frac{cos t}{1+cos t},dt= int_0^{frac{pi}{2}}left(frac{1+cos t}{1+cos t}-frac{1}{1+cos t}right),dt$$ $$Rightarrow I=frac{pi}{2}-frac{1}{2}int_0^frac{pi}{2}frac{1}{cos^2frac{t}{2}},dt=frac{pi}{2}-1$$
edited Dec 23 '18 at 18:58
answered May 13 '18 at 11:45
ZackyZacky
7,59511061
7,59511061
add a comment |
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