solve the equation 8xsquared+2x-3=0 hence solve the equation 8cos^2y+2cosy_3=0 for the range 0degrees

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solve the equation 8xsquared+2x-3=0 hence solve the equation 8cos^2y+2cosy_3=0 for the range 0degrees <y <180

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    2021-09-09T15:56:13+00:00

    8x^2 + 2x – 3 = 0

    (4x         )(2x      )

    (4x + 3)(2x – 1) = 0

    Surprise: that might actually work.

    4x + 3 =0

    4x = – 3

    x = – 3/4    That would be between 90 and 180 because the cos(x) is minus in quad 2.

    2x – 1 = 0

    2x = 1

    x = 1/2        This one is actually only in quad 1.

    cos(y) = 1/2

    y = 60 degrees.

    cos(y) = – 3/4

    y = 138.6 degrees. You could do this by

    cos(y) = 3/4

    cos(y) = 41.4 degrees. Because the 3/4 is minus, the angle is in quad 2

    180 – 41.4 = 138.6. Same answer.

    The calculator does in the following way.

    2nd F

    Cos-1(

    – 0.75

    )

    =

    which will give you 138.6 immediately.

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