You don’t have to worry about identity thief
" the product " means multiply
(2ab + b)(a^2 - b^2) = 2a^3b - 2ab^3 + a^2b - b^3
when multiplied : (2a + b)(2a^3b - 2ab^3 + a^2b - b^3) =
4a^4b - 4a^2b^3 + 2a^3b - 2ab^3 + 2a^3b^2 - 2ab^4 + a^2b^2 - b^4
...result is a polynomial with 8 terms
Recall that sin²Ф+cos²Ф=1,
so cos²Ф=1-sin²Ф=(1+sinФ)(1-sinФ)
the (1-sinФ) in the numerator cancel with the (1-sinФ) in the denominator, the result is 1+sinФ
