Asked by cassy
4cos^2x-5sinxcosx-6=0
find the x :( please
find the x :( please
Answers
Answered by
Steve
since cos2x = 2cos^2 x - 1, we have
2cos2x - 5/2 sin2x - 4 = 0
or
4cos2x - 5sin2x - 8 = 0
4cos2x = 5sin2x + 8
16cos^2 2x = 25sin^2 2x + 80sin2x + 64
16 - 16sin^2 2x = 25sin^2 2x + 80sin2x + 64
41sin^2 2x + 80sin2x + 48 = 0
now just solve for sin2x using the quadratic formula.
2cos2x - 5/2 sin2x - 4 = 0
or
4cos2x - 5sin2x - 8 = 0
4cos2x = 5sin2x + 8
16cos^2 2x = 25sin^2 2x + 80sin2x + 64
16 - 16sin^2 2x = 25sin^2 2x + 80sin2x + 64
41sin^2 2x + 80sin2x + 48 = 0
now just solve for sin2x using the quadratic formula.
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