Monday, September 7, 2015

`int cot^5(theta) sin^4(theta) d theta` Evaluate the integral

`intcot^5(theta)sin^4(theta)dTheta=`


`int[(cos^5(theta))/(sin^5(theta))]sint^4(theta)dTheta=`


`int[(cos^5(theta))/(sin^(theta))]d(Theta)=`


`intcos^4(theta)[cos(theta)/sin(theta)]d(Theta)=`


`int(cos^2(theta))^2[cos(theta)/sin(theta)]d(Theta)=`


`int(1-sin^2(theta))^2[cos(theta)/sin(theta)]d(Theta)=`


Integrate using u-subsitution.


Let 


`u=sin(theta)`


`(du)/[d(theta)]=cos(theta)`


`d(theta)=(du)/[cos(theta)]`



`int(1-u^2)^2[cos(theta)/u][(du)/(cos(theta))]=`


`int[1-2u^2+u^4]/udu=`


`int[(1/u)-2u+u^3]du=`


`ln|u|-(2u^2)/2+u^4/4+C=`


`ln|u|-u^2+1/4u^4+C=`


`ln|sin(theta)|-sin^2(theta)+1/4sin^4(theta)+C`



The final answer is:  `ln|sin(theta)|-sin^2(theta)+1/4sin^4(theta)+C `

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