Find the value (up to decimal places) of
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First we will write :
cot − 1 ( x 2 − x + 1 ) = tan − 1 ( x 2 − x + 1 ) 1 = tan − 1 1 + x ( x − 1 ) 1 = tan − 1 1 + x ( x − 1 ) x − ( x − 1 ) = tan − 1 x − tan − 1 ( x − 1 )
Our integral becomes I = ∫ 0 1 cot − 1 ( x 2 − x + 1 ) d x = ∫ 0 1 tan − 1 x d x − ∫ 0 1 tan − 1 ( x − 1 ) d x
Also in the integral ∫ 0 1 tan − 1 ( x − 1 ) d x we put t = 1 − x we get it as : − ∫ 0 1 tan − 1 t d t
I = 2 ∫ 0 1 tan − 1 x d x
Put x = t a n θ to get I = 2 ∫ 0 π / 4 θ s e c 2 θ d θ
Apply integration by parts to get I = 2 ( θ t a n θ ∣ 0 π / 4 − ∫ 0 π / 4 t a n θ d θ ) = 2 ( 4 π − 2 1 l n ( 2 ) ) = 2 π − l n ( 2 )