math(Trigonometry)

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2cos^2 theta + 5 sin theta - 4 = 0

  • math(Trigonometry) -

    2(1-sin^2) + 5sin - 4 = 0
    2sin^2 - 5sin + 2 = 0
    (2sin-1)(sin-2) = 0
    sin = 1/2 or 2
    ...

  • math(Trigonometry) -

    can give me a further and detail explanation where did the theta on the 5 and the formula on changing the cos theta.

  • math(Trigonometry) -

    you know that cos^2 = 1-sin^2
    the rest is just algebra I
    I dropped the thetas just for ease of typing.

    Naturally, sin can never be 2, so that's a non-solution, even though it does satisfy the original equation.

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