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January 31, 2015

January 31, 2015

Posted by **Katlynn** on Wednesday, March 6, 2013 at 9:55pm.

cos(x)(9cos(x) + 4) = 4; [0, 2π)

- Trigonometry -
**Reiny**, Thursday, March 7, 2013 at 8:55amexpand first

9cos^2 x + 4cosx - 4 = 0

let y = cosx

9y^2 + 4y - 4 = 0

y = (-4 ±√160)/18 , using the formula

= (-4 + 4√10)/18

= (-2 ± 2√10)/9

= appr .480506 or appr -.92495

then cosx = .480506 or cosx = -.92495

x = 61.28° or 298.72° or 157.66° or 202.34°

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