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Thread: I can't think tonight or something

  1. #51
    Registered Users Regular ElijahWyatt's Avatar
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    sin(arcsin(8x))
    thats 8x
    "As for me, all i know is that i know nothing"

  2. #52
    what about .. eyebrows God's Avatar
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    Quote Originally Posted by ElijahWyatt View Post
    arccos(2x)=arcsec(2x)
    arcsec(x) = arccos(1/x) so
    arccos(2x)=arccos(1/2x)
    cos both sides.
    2x=1/2x
    4x^2=1
    x=1/4
    x = multiples of pi/2

  3. #53
    what about .. eyebrows God's Avatar
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    lol i did that wrong. its 1 or -1

  4. #54
    what about .. eyebrows God's Avatar
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    actually 1/2 or -1/2, you know what i mean

  5. #55
    Registered Users Regular ElijahWyatt's Avatar
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    why? What was wrong with my "proof"?
    and i'm right btw
    arccos(1/2)= 0 rads
    arcsec(1/2)= 0 rads.
    Meaning my answer of x=1/4 is right.

    but ya, -1/4 too, because square root.
    "As for me, all i know is that i know nothing"

  6. #56
    what about .. eyebrows God's Avatar
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    you actually did it right looking at it, but you didnt actually take the square root

  7. #57
    princeso Kirby's Avatar
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    Ok I got all these now except for one, God was right the whole time lol.

    The only one I can't figure out is:

    Let f(x)=3x^5+x^3+1
    f^-1(5)

    I can't think of an easy way to do this besides switching the x and y, then right off the bat plugging in 5, which doesn't work.

  8. #58
    princeso Kirby's Avatar
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    Yeah I go in giant circles:

    (1) 3x^5 - x^3 = y + 1
    (2) x^3(x-1) = y + 1
    (3) x-1 = (y+1)/x^3
    (4) x = (y+1)/x^3 + 1
    (5) x/(y+1) = 1/x^3 + 1/(y+1)
    (6) x/(y+1) - 1/(y+1) = 1/x^3
    (7) x^4/(y+1) - x^3/(y+1) = 1
    (8) (x^4-x^3)/(y+1) = 1
    (9) x^3(x-1) = y+1 (step 2)

  9. #59
    what about .. eyebrows God's Avatar
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    you won't be able to find an explicit formula for the inverse of a quintic. well, maybe you CAN, but it's pretty advanced stuff. i think. so just look for the value of x that will make f = 5.

  10. #60
    princeso Kirby's Avatar
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    Yeah I emailed by professor and that is exactly what he said, "just plug in common numbers"...

    the answer is one

    ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh!

  11. #61
    princeso Kirby's Avatar
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    I feel like I am being trolled.

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