1.Найдите -47cos2α, если cosα=-0,42. Найдите значение выражения (5sin74°)/(cos...

$1)\\ cosa=-0.4\\ -47*cos2a=-47(2cos^2a-1)=-47(2*(-0.4)^2-1)=31.96$
$2)\\ \frac{5sin74}{cos37*cos53}=\frac{5sin74}{\frac{cos90+cos16}{2}}=\\\\ \frac{10sin74}{cos110+cos16}=\frac{10cos16}{cos16}=10$

$\frac{5sin98}{sin49*sin41}=\frac{5*sin98}{\frac{cos8-cos90}{2}}=\\\\ \frac{10sin98}{cos8}=\frac{10cos8}{cos8}=10$


$\frac{3sina-5cosa+2}{sina+3cosa+6}=\frac{1}{3}\\ 9sina -15cosa+6=sina+3cosa+6\\ 8sina-18cosa=0\\ 8sina=18cosa\\ tga=\frac{18}{8}=\frac{9}{4}$