Question

cos(a+b)+2sina*sinb/cos(a-b)

Answer 1

=(cos a * cos b - sin a * sin b + 2 sin a *sinb )/cos(a-b)=(cos a * cos b + sin a * sin b )/cos ( a- b)=cos(a-b) / cos (a-b)= 1

Answer 2

спасибо)