Question

sin a +cos a=5/7
найти: tga*cos^2 a

Answer 1

$tg alpha *cos^{2} alpha =sin alpha *cos alpha \ (sinalpha +cosalpha)^{2} =( frac{5}{7} )^{2} \ 1+2sin alpha *cos alpha= frac{25}{49} \ 2sin alpha *cos alpha=- frac{24}{49} \ sin alpha *cos alpha=-frac{12}{49}$