Question

evaluate
sin35°sin55°- cos35°cos55°

Answer 1

since cos (a+b) =- (sin a sinb - cos a cos b)
so cos (35+55) = -(sin35 sin 55- cos 35 cos 55)
so = - cos 90= 0

Answer 2

Given Equation is sin35sin55 - cos35 cos55.

sin35 sin(90 - 35) -  cos 35 * cos(90 - 35)

sin35 * cos 55 - cos 35 * sin35

-cos(35 + 55)

-cos(90)

0.


Hope this helps!