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January 21, 2017
Posted by **Sandy** on Monday, March 8, 2010 at 1:25pm.

2 cos^2 x + cos x = 1

- trig -
**Damon**, Monday, March 8, 2010 at 4:49pm2 y^2 + y = 1

y^2 + (1/2)y = 1/2

y^2 + (1/2)y + 1/16 = 8/16+1/16 = 9/16

(y+1/4)^2 = 9/16

y+1/4 = -3/4 or +3/4

y = -1 or 1/2

so

cos x = -1 or cos x = 1/2

find all those places for example cos pi = -1 and cos pi/3 or 60 degrees = 1/2 as does cos of -pi/3 which is 5pi/3