Question

1/cos^2альфа. -1 при альфа =Π/3

Answer 1

$frac{1}{cos^2( alpha )-1}=- frac{1}{1-cos^2( alpha )}=- frac{1}{sin^2( alpha )} = - frac{1}{[sin( frac{pi}{3} )]^2} =- frac{1}{[ frac{ sqrt{3} }{2} ]^2}= - frac{1}{ frac{4}{3} }=$

$=- frac{3}{4}=-0.75$