Question

ДАЮ 40 БАЛЛОВ СРОЧНО

Answer 1

$4)\; \; cos^2a=\frac{3}{5}\\\\10cos^2a-sin^2a=10cos^2a-(1-cos^2a)=11cos^2a-1=11\cdot \frac{3}{5}-1=\frac{28}{5}$

$5)\; \; sina=-\frac{3}{7}\\\\cos2a=cos^2a-sin^2a=(1-sin^2a)-sin^2a=1-2sin^2a=1-2\cdot \frac{9}{49}=\frac{31}{49}$

$6)\; \; -\frac{1}{2}cos^2x+0,5-0,5sin^2x=-0,5\cdot (\underbrace {sin^2x+cos^2x}_{1})+0,5=\\\\=-0,5+0,5=0$

$6b)\; \; cos(-60^\circ )+cos150^\circ =cos60^\circ +cos(180^\circ -30^\circ )=\\\\=\frac{1}{2}-cos30^\circ =\frac{1}{2}-\frac{\sqrt3}{2}=\frac{1-\sqrt3}{2}$