Question

(sin^4a - cos^4a)/sin a cos a

Answer 1

$frac{sin^{4}a-cos^4a}{sina*cosa} = frac{(sin^{2}a-cos^2a)(sin^{2}a+cos^2a)}{sina*cosa} = frac{sin^{2}a-cos^2a}{sina*cosa} = frac{-cos2x}{ frac{sin2x}{2} } =$$-2ctg2x$