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Find the mistake of the following evaluation of the integral`I=int_0^pi(dx)/(1+2sin^2x)``I=int_0^pi(dx)/(cos^2x+3sin^2x)``=int_0^pi(sec^2x dx)/(1+3tan^2x)=1/(sqrt(3))[tan^(-1)(sqrt(3)tanx)]pi0=0` |
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Answer» Here the anti derivative `1/(sqrt(3))[tan^(-1)(sqrt(3)tanx)]=F(x)` is discontinuous at `x=pi//2` in the interval `[0,pi]`. Since `F((pi^(+))/2)=lim_(hto0)F((pi)/2+h)` `=lim_(hto0)(1/(sqrt(3)))tan^(-1){sqrt(3)"tan"(1/2pi+h)}` `=lim_(hto0)(1//sqrt(3))"tan"^(-1){-sqrt(3)coth}` `=(1/(sqrt(3))) tan^(-1)(-oo)=-pi//(2sqrt(3))` and `F(1/2pi-0)=pi//(2sqrt(3))!=F(1/2pi+0)` the second fundamental theorem of integral calculus is not applicable. |
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