Question

Найдите 2cos2a,если sin a=-0,7

Answer 1

$2cos2a-?\\sina=-0,7\\\\sin^2a=(-0,7)^2=0,49\\cos^2a=1-sin^2a=1-0,49=0,51\\\\2cos2a=2(cos^2a-sin^2a)=2(0,51-0,49)=2*0,02=0,04$