Question

cosA * cosB - cos ( A + B) / sin A * sinB - cos (A-B)

Answer 1

$frac{cosAcdot cosB-cos(A+B)}{sinAcdot sinB-cos(A-B)}=frac{cosAcdot cosB-(cosAcdon cosB-sinAcdot sinB)}{sinAcdot sinB-(cosAcdot cosB+sinAcdot sinB)}=\\=frac{sinAcdot sinB}{-cosAcdot cosB} =-tgAcdot tgB$