Question

помогите решить, вычислите cos 5-2*sin25*sin20

Answer 1

0.996-2*0.4226*0.342=0.996-0.48653=0.50947=cos1

Answer 2

$<var>cos5-2*sin25*sin20= \\ \\ =cos5-2(\frac{1}{2}[cos(25-20)-cos(25+20)])= \\ \\ = cos5-cos5+2cos45=2*\frac{\sqrt2}{2}=\sqrt2</var>$