Question

Use an appropriate identity to find the exact value of the expression.

cos(310)cos(50)-sin(310)sin(50)

Answer 1

We know that cos(a+b) = coa.cob-sia.sinb

cos(310+50) = coas(310).cos(50) -sin(310).sin(50)

1st) cos(310+50) cos(360) = 1

2nd) cos (310) = cos(50) and sin(310) = -sin(50)

3rd) 1= cos²(50) - [-sin²(50)]

1= cos²(50) + sin²(50)
, which is 1