How do you solve $4 cos^2 (2x + pi) = 3$ ?

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Answer 1 · 2015-08-29T05:40:41

Solve 4cos^2 (2x + pi) = 3

Ans: -75 and -105 deg

$4cos^2 (2x + pi) = 3$
$cos^2 (2x + pi) = 3/4 = 0.75$
$cos (2x + pi) = +- 0.866$
$2x + 180 = +- 30$ deg

a. 2x + 180 = 30 --> 2x = 30 - 180 = - 150 --> $x = -75$ deg
b. 2x + 180 = - 30 --> 2x = -30 - 180 = -210 $deg -> ->$ x = - 105# deg

How do you solve 4 cos^2 (2x + pi) = 34 cos^2 (2x + pi) = 3?