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Math Help - which rule to use for this equation?

  1. #1
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    which rule to use for this equation?

    y = x^4 - 4x^3 - 2 cos (x) + tan (x)

    question asks to differentiate the following function

    the answer i believe is 4x^3 - 16x^2 + 2 sin (x) + tan (x)

    do i have the correct answer?
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by JontyP View Post
    y = x^4 - 4x^3 - 2 cos (x) + tan (x)

    question asks to differentiate the following function

    the answer i believe is 4x^3 - 16x^2 + 2 sin (x) + tan (x)

    do i have the correct answer?
    no, the derivative of tan(x) is not tan(x)

    why do you feel tan(x) should stay the same?
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  3. #3
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    oops i missed out the last bit of the answer!

    it should look like this
    4x^3 - 12x^2 + 2 sin (x) + (1/cos^2(x))

    i've changed the -16x^2 to a -12 too
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  4. #4
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by JontyP View Post
    oops i missed out the last bit of the answer!

    it should look like this
    4x^3 - 12x^2 + 2 sin (x) + (1/cos2(x))

    i've changed the -16x^2 to a -12 too
    that's correct now. by the way, we can write \frac 1{\cos^2 x} as \sec^2 x
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