How do you solve 5cos(2x)+1=3cos(2x)5cos(2x)+1=3cos(2x) and find all general solutions?

1 Answer
Jan 23, 2017

pi/3 = kpπ3=kp
(5pi)/3 + kpi5π3+kπ

Explanation:

5cos 2x + 1 = 3cos 2x
2cos 2x = - 1
cos 2x = - 1/2
Trig table and unit circle give 2 solution arcs:
2x = +- (2pi)/3 + 2kpi2x=±2π3+2kπ --> x = +- (2pi)/6 + kpi = +- pi/3 + kpix=±2π6+kπ=±π3+kπ
The arc (5pi)/35π3 is co-terminal to the arc (- pi)/3π3.
General answers:
x = pi/3 + kpix=π3+kπ
x = (5pi)/3 + kpix=5π3+kπ