SOLUTION: Determine the general solution if:cos2x-5cosx-2=0

Question 1023620: Determine the general solution if:cos2x-5cosx-2=0
Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
Hi there,
cos2x-5cosx-2=0
(cos2x = 2cos^2 - 1)
2cos^2x - 1 - 5cosx - 2
2cos^2x - 5cosx - 3 = 0
(2cosx + 1)(cosx - 3)= 0
cosx - 3 = 0
cosx = 3 (Discount as cosx only
goes up to 1 and down to -1)
2cosx + 1 = 0
2cosx = -1
cosx = -1/2
x = 120 and 240 degrees
x = 2pi/3 or 4pi/3
Hope this helps :-)
RELATED QUESTIONS
Determine the general solution for cos2x - 2sin2x = -1 (answered by Alan3354)

Determine the general solution of: cos2x 4sin^2x-5sinx-4=0 (answered by Alan3354)

Please Find the general solution of: sin3x-sinx=... (answered by ikleyn)

Solve for x on the interval given: a) 2sin^2x-5cosx+1=0 [0, pie] b) sinx/2=0 [-pie,... (answered by Alan3354)

Determine cos2x if sin^4 x = 25/36, the solution is in the first... (answered by reviewermath)

prove the following identity 1. cos^2 3x - cos6x = sin^2 3x find the general... (answered by ikleyn)

Determine the general solution to the equation... (answered by MathLover1,ikleyn)

what is the general solution of... (answered by jsmallt9)

Hey, if you can please help me solve this that would be great thank you! Determine... (answered by ikleyn)