answer will be pi/4 ..see we have to use the property of definite integral f(a-x) = f(x).
also change tanx to sinx / cosx
now we have pi/2∫0 dx/1 + tan x = pi/2∫0 dx/ (1 + (sinx/cosx) ) = pi/2∫0 (cosx)dx /(sinx + cosx)
now apply f(a-x) = f(x). therfore we get ½ pi/2∫0 (cosx + sinx )dx /(sinx + cosx) = 1/2* [1]pi/2 = pi/4
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