SOLUTION: Hello, I have to find a trig equation for all the values of theta (0< x < 2pi) (< = less than or equal to). The problem is 7cos^2theta-1 = 5costheta. I got .88 and -.16 but thos

Question 966067: Hello,
I have to find a trig equation for all the values of theta (0< x < 2pi) (< = less than or equal to). The problem is 7cos^2theta-1 = 5costheta. I got .88 and -.16 but those answers are wrong. Any help would be greatly appreciated. Thanks!
K.Legters
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
7cos^2theta-1 = 5costheta
7cos^2(x)-1 = 5cosx
solve for cos x using quadratic formula:
7cos^2(x)-5cosx-1=0

a=7,b=-5, c=-1
ans:
a=7,b=-5, c=-1
ans:

cosx=0.877
x=0.50, 5.78(In quadrants I and IV where cos>0)
or
cosx=-0.16
x=1.73, 4.55 (In quadrants II and III where cos<0)
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