SOLUTION: In the interval 90degrees <= x <= 180degrees find the value of x that satisfies the equation 2cos^2x = 1 I started by dividing both sides by 2cos^2 which left me with X =

Algebra ->  Trigonometry-basics -> SOLUTION: In the interval 90degrees <= x <= 180degrees find the value of x that satisfies the equation 2cos^2x = 1 I started by dividing both sides by 2cos^2 which left me with X =      Log On


   

Question 278802: In the interval 90degrees <= x <= 180degrees find the value of x that satisfies the equation 2cos^2x = 1
I started by dividing both sides by 2cos^2 which left me with
X = 1/2cos^2 now I'm stuck
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
You can't divide by 2cos^2 because cos(x) is the function.
Do a substitution and you'll see what I mean.
Let
Z=cos%28x%29
2%2AZ%5E2=1
Z%5E2=1%2F2
Z=+0+%2B-+sqrt%282%29%2F2
Now substitute back,
cos%28x%29=0+%2B-+sqrt%282%29%2F2
In the region of interest 90%3Cx%3C180,
cos%28x%29+%3C=+0
Then
cos%28x%29=-sqrt%282%29%2F2
x=135