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cos2x-sinx=0. Factor and solve for sinx

  • math -

    1 - 2sin^2 x - sinx = 0
    2sin^2 x + sinx - 1 = 0
    (2sinx - 1)(sinx + 1) = 0
    sinx = 1/2 or sinx = -1

    in degrees, x = 30° , 150° , 270°
    in radians, x = π/5 , 5π/6 , 3π/2

  • math -

    Thanks. I was wondering, why is it "+ sin x" in the second step?

  • math -

    do you just change all the signs of the terms? if so, why is this necessary?

  • math -

    I multiplied each term by -1
    (notice all the signs have switched)

    I like my quadratics to start with a positive coefficient, although that would not be necessary.
    It just makes it easier to factor.

  • math -

    ok thank you.

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