Question

sina+cosa=a

sina*cosa=?

Answer 1

Объяснение:

$sin\alpha +cos\alpha =a\ \ \ \ \ sin\alpha *cos\alpha =?\\(sin\alpha +cos\alpha )^2=a^2\\sin^2\alpha +2*sin\alpha *cos\alpha +cos^2\alpha =a^2\\1+2*sin\alpha*cos\alpha =a^2\\2*sin\alpha *cos\alpha =a^2-1\ |:2\\sin\alpha *cos\alpha =\frac{a^2-1}{2} .$