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Prove that the derivative of tan(2x) - cot(2x) equals...

  1. Aug 14, 2015 #1
    Let f(x) = tan(2x) - cot(2x) defined on x∈]0,π/4[

    Prove that derivative of f(x) is 16/1-cos(8x)

    What I did was:

    2 * Sin^2(2x) + 2 * Cos^2(2x) / Cos^2(2x) + Sin^2(2x)

    If I factor the 2, I reach:

    2 * (Sin^2(2x) + Cos^2(2x) / 1+cos(4x)/2 + 1-cos(4x)/2

    2 * 1/ 1 = 2?

    What went wrong?
  2. jcsd
  3. Aug 14, 2015 #2


    Staff: Mentor

    Did you really mean to write ##\frac{16}{1} - cos(8x)##? If not, use parentheses around the terms in the denominator.
    Show how you got this. Also, when the numerator or denominator of a fraction has two or more terms, you must put parentheses around them.
  4. Aug 14, 2015 #3
    Okay, nvm, solved it.

    In the denominator, I turned the multiplication to addition, which is why I got a wrong result.
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