math

Give that x is angle in the first quadrant such that 8sin 2x + 2cosx – 5 = 0
Find:
cosx
tanx

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  1. 8sin2x + 2cosx - 5 = 0
    16 sinx cosx + 2cosx - 5 = 0
    16sinx cosx = 5 - 2cosx
    256 sin^2x cos^2x = 25 - 20cosx + 4cos^2x
    256cos^2x - 256cos^4x = 25 - 20cosx + 4cos^2x

    256cos^4x - 252cos^2x - 20cosx + 25 = 0

    I don't see any easy roots there, so a graphical approach may be your best bet.

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