1.

Consider the integral `I=int_(0)^(2pi)(dx)/(5-2cosx)` Making the substitution `"tan"1/2x=t`, we have `I=int_(0)^(2pi)(dx)/(5-2cosx)=int_(0)^(0)(2dt)/((1+t^(2))[5-2(1-t^(2))//(1+t^(2))])=0` The result is obviously wrong, since the integrand is positive and consequently the integral of this function cannot be equal to zero. Find the mistake.

Answer» Correct Answer - 2
Here the mistake lies in the substitution `"tan"1/2x=t`, because `"tan"1/2x` is discontinuous at `x=pi` which is a point in the interval `[0,2pi]`.


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