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rubyhunter

  • 3 years ago

if cos x = 4/11 find cos 2A (HELP PLEASE)

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  1. maym0Re97
    • 3 years ago
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    by 2A do you mean 2x?

  2. maym0Re97
    • 3 years ago
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    If that's the case, then your'e going to do arc cos of 4/11, which yields x, then plug that value of x into cos2x

  3. rubyhunter
    • 3 years ago
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    i dnt get ti can you walk me through it

  4. maym0Re97
    • 3 years ago
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    ok so by 2A did you actually mean cos2x?

  5. rubyhunter
    • 3 years ago
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    yes

  6. shubhamsrg
    • 3 years ago
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    why dont you simply use this gem of a formulla : cos 2x = (2cos^2 x) - 1 hope this helps..

  7. rubyhunter
    • 3 years ago
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    no it doesnt help CAUSE I DNT KNOW HOW TO DO IT :(

  8. shubhamsrg
    • 3 years ago
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    nevermind,,i cant help you further then :/

  9. maym0Re97
    • 3 years ago
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    Ok so use your graphing calculator and there should be a button that's like cos, and right above it you'll see cos^-1. Plug into your calcultar, cos^-1(4/11), because what that's saying is cos of the whatever that is, is going to be 4/11. Now you have x. Now plug whatever you got for x back into your calculator.

  10. maym0Re97
    • 3 years ago
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    Back into the equation cos2x.

  11. rubyhunter
    • 3 years ago
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    wait y am i doin cos-1 instead of cos

  12. maym0Re97
    • 3 years ago
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    because that's how you're going to find x. It's just like how if you had x^2=4, you'd find the square root of both sides. In this case you're getting rid of the cos.

  13. rubyhunter
    • 3 years ago
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    so 68,67631374

  14. rubyhunter
    • 3 years ago
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    what do i do after

  15. maym0Re97
    • 3 years ago
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    ok, so is that what you're getting for cos^-1(4/11)?

  16. rubyhunter
    • 3 years ago
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    yea

  17. maym0Re97
    • 3 years ago
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    ok you have that value for x, now plug that in for x in cos2x. So plug in cos(2*68.67). That SHOULD be how you do it, I haven't done stuff like this in two years.

  18. rubyhunter
    • 3 years ago
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    so is it a -.7353878608

  19. maym0Re97
    • 3 years ago
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    Yeah uhhhh that should be it, apologies if it isn't though, I don't have a calculator with me.

  20. jishan
    • 3 years ago
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    use to apply cos2x=cos^2x-sin^2x cox=4/11 sinx=squareroot( 1-cos^2x)

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