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`(1-tan^2 theta)/(cot^2-1) = tan^2 theta`
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LHS = `(1- tan^2 theta)/(cot^2 theta-1)`
=`(1-(sin^2 theta)/(cos^2 theta))/((cos^2 theta )/(sin^2 theta)-1)`
=`((cos^2 theta - sin^2 theta)/(cos^2 theta))/((cos^2theta-sin^2 theta)/(sin^2 theta))`
=`(sin^2 theta)/(cos^2 theta)`
= tan2 ЁЭЬГ
= RHS
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