Question

1)  cos6άcos4ά-sin6άsin4ά 

2)  sin14°cos31°+cos14°sin31°

Answer 1

1. $cos6a*cos4a-sin6a*sin4a = cos(6a+4a) = cos10a$

2. $sin14`cos31`+cos14`sin31` = sin(14`+31`) = sin45` = sqrt{2}/2$