Answer:
1 + cosa sina
Explanation:
cos³a - sin³a ← is a difference of cubes and factors in general as
a³ - b³ = (a - b)(a² + ab + b²) , then
cos³a - sin³a
= (cosa - sina )(cos²a + cosa sina + sin²a)
= (cosa - sina)(1 + cosa sina) [ sin²a + cos²a = 1 ]
Then
=
← cancel (cosa - sina) on numerator/ denominator
= 1 + cosa sina