Monday, April 18, 2011

`int sin^-1 x dx` Evaluate the integral

`intsin^-1xdx`


If f(x) and g(x) are differentiable functions, then


`intf(x)g'(x)dx=f(x)g(x)-intf'(x)g(x)dx`


If we write f(x)=u and g'(x)=v, then


`intuvdx=uintvdx-int(u'intvdx)dx`


Using the above method of integration by parts,


`intsin^-1xdx=sin^-1x*int1dx-int(d/dx(sin^-1x)int1dx)dx`


`=sin^-1x*x-int(1/sqrt(1-x^2)*x)dx`


`=xsin^-1x-intx/sqrt(1-x^2)dx`


Now evaluate using the method of substitution,


Substitute `t=1-x^2,=> dt=-2xdx`


`intx/sqrt(1-x^2)dx=intdt/(-2sqrt(t))`


`=-1/2intdt/sqrt(t)`


`=-1/2(t^(-1/2+1)/(-1/2+1))`


`=-1/2(t^(1/2)/(1/2))`  


`=-t^(1/2)`


substitute back `t=1-x^2`


`=-(1-x^2)^(1/2)`


`intsin^-1xdx=xsin^-1x-(-(1-x^2)^(1/2))`


adding constant C to the solution,


`=xsin^-1x+sqrt(1-x^2)+C`

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