SOLUTION: Cos2A=cosA find values of A in 0<A<360

Question 864223: Cos2A=cosA find values of A in 0
Answer by hamsanash1981@gmail.com(151) (Show Source): You can put this solution on YOUR website!
cos2A = cosA
2cos^2A -1 = cosA Since cos2A = 2cos^2A-1
2cos^2A - 1 - cosA = 0
Let x = cosA
then
2x^2 -x - 1 = 0
2x^2 -2x +1x -1 = 0
2x(x- 1) +1 (x -1) = 0
(2x + 1) (x-1) = 0
2x +1 = 0 x-1 =0
2cosA= -1, cosA = 1
cosA = -1/2, cosA = cos0
cosA = - (cos 60), A = 0
- value lies on second quadrant hence A = 180 - 60
A = 120
therefore the values of A are 0, 120.

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