Why foil?

Use the difference of two square formula,

(2(1-sinx)(1+sinx)) = 2(1-sin^2 x) = 2cos^2 x

Of course, you may FOIL, if you do not remember formula. But rational and faster way is to use the formula.
Now then:
(a - b)(a + b) = a² - b²
sin²x + cos²x = 1 --------> 1 - sin²x = cos²x

Rest is in the Robert's work ...........