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shaqadry

  • 3 years ago

solve 3 sin^2 x - 2 = cos x

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  1. tyteen4a03
    • 3 years ago
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    Remember that \(sin^2(x) + cos^2(x) = 1\).

  2. shaqadry
    • 3 years ago
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    yes...

  3. ashwinjohn3
    • 3 years ago
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    Is 3 sin^2(x-2)=cos x

  4. tyteen4a03
    • 3 years ago
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    @ashwinjohn3 I believe it's 3sin^2(x) - 2.

  5. shaqadry
    • 3 years ago
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    yea its 3 sin^2 (x) - 2 = cos (x)

  6. hartnn
    • 3 years ago
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    change sin^2 x to cos^2 x using \(\sin^2(x) + \cos^2(x) = 1\) then if you put cos^2 x = y, you'll get a quadratic in y.

  7. ashwinjohn3
    • 3 years ago
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    ok... then,here \[\sin ^{2} x=1-\cos ^{2} x\] \[3 (1-\cos ^{2}x )-2=3-3 \cos ^{2}x -2=1-3\cos ^{2}x\]

  8. shaqadry
    • 3 years ago
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    thats what i get but then i cant figure out how to solve the angle :/

  9. hartnn
    • 3 years ago
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    put cos x =y, then you get a quadratic in y..

  10. ashwinjohn3
    • 3 years ago
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    But \[1=\cos ^{2}x+\sin ^{2} x\] =\[\sin ^{2}x+\cos ^{2}x-3\cos ^{2}x=\sin ^{2}x-2\cos ^{2}x\]

  11. hartnn
    • 3 years ago
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    ?

  12. hartnn
    • 3 years ago
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    \(3 \sin^2 x - 2 = \cos x \\ 1-3\cos^2x = \cos x \\ 1-3y^2 =y. \\ 3y^2 +y-1=0 \) can you solve this quadratic ?

  13. shaqadry
    • 3 years ago
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    yeaaa but by using calculator, the answer is in decimal point. is there any other way i can calculate the angle?

  14. hartnn
    • 3 years ago
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    you'll get same answer using any other method, that you got on calculator. whatever you got, equate it to y= ..., ... so, cos x = ... , .... then take cos^{-1} (or arccos) of those 2 values ("decimal values"), using calculator, and ou'll get 2 angles.

  15. hartnn
    • 3 years ago
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    you might be getting, -0.767 and 0.434 then 2 angles will be cos^{-1}(-0.767) and cos^{-1}(0.434) calculate those using calculator.

  16. shaqadry
    • 3 years ago
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    hmmm okay thanks

  17. hartnn
    • 3 years ago
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    welcome :)

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