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how do you foil (2(1-sinx)(1+sinx))

how do you foil when theres a coefficient?

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2 Answers

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 ...........