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12sin^2+cos-6=0 I'm having trouble solving this the proper way. Please help. Thanks?

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  • Troy
    Lv 6
    4 years ago
    Favorite Answer

    Sin^2 = 1 - cos^2

    12[1-cos^2] + cos -6 =0

    12 cos^2 -cos -6 =0

    Solve this equation for cos as you would any quadratic equation.

  • ?
    Lv 7
    4 years ago

     

    Maybe the reason you are having trouble is because you don't even have a variable.

    12sin^2 + cos - 6 = 0 ----> this makes no sense.

    12sin^2x + cosx - 6 = 0 ----> now this makes sense.

    Anyway, replace sin^2x with 1 - cos^2x to get an equation using only cosx

    This will make it easier to solve, by factoring or using quadratic formula.

    12 sin²x + cosx − 6 = 0

    12 (1 − cos²x) + cosx − 6 = 0

    −12 cos²x + cosx + 6 = 0

    12 cos²x − cosx − 6 = 0

    12 cos²x − 9 cosx + 8 cosx − 6 = 0

    3 cosx (4 cosx − 3) + 2 (4 cosx − 3) = 0

    (4 cosx − 3) (3 cosx + 2) = 0

    cosx = 3/4 or −2/3

    cosx = 3/4 ------> x = 2πk ± cos⁻¹(3/4)

    cosx = −2/3 ----> x = 2πk ± cos⁻¹(−2/3)

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