SOLUTION: solve equation for solution (0 deg, 360 deg) 4 cos ^2 theta +4 cos theta = 1. I used the quadratic formula, but get stuck.

Algebra ->  Trigonometry-basics -> SOLUTION: solve equation for solution (0 deg, 360 deg) 4 cos ^2 theta +4 cos theta = 1. I used the quadratic formula, but get stuck.      Log On


   

Question 955450: solve equation for solution (0 deg, 360 deg) 4 cos ^2 theta +4 cos theta = 1.
I used the quadratic formula, but get stuck.
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
solve equation for solution (0 deg, 360 deg) 4 cos ^2 theta +4 cos theta = 1
4cos^2(x)+4cosx=1
4cos^2(x)+4cosx-1=0
solve for cosx by quadratic formula:
cosx+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a=4, b=4, c=-1
ans:
cosx=-1.207 (reject)(-1 ≤ cosx ≤1)
or
cosx=0.207
x≈78.05˚, 281.95˚