Question

Докажите тождество ctga*ctgb-1=cos(a+b)/sina*sinb ,a-альфа,b-бетта

Answer 1

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