Question

Докажите тождество .файл прикреплен

Answer 1

Привет!

$\frac{cos(a+b)+cos(a-b)}{cos(a-b)-cos(a+b)} =\frac{cos(a)cos(b)-sin(a)sin(b)+cos(a)cos(b)+sin(a)sin(b)}{cos(a)cos(b)+sin(a)sin(b)-cos(a)cos(b)+sin(a)sin(b)} =\frac{2cos(a)cos(b)}{2sin(a)sin(b)} =\frac{cos(a)cos(b)}{sin(a)sin(b)} =ctg(a)*ctg(b)$