- #1

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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?

- Thread starter NooDota
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- #1

- 68

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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

Mark44

Mentor

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Did you really mean to write ##\frac{16}{1} - cos(8x)##? If not, use parentheses around the terms in the denominator.Let f(x) = tan(2x) - cot(2x) defined on x∈]0,π/4[

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

Show how you got this. Also, when the numerator or denominator of a fraction has two or more terms, youNooDota said:What I did was:

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

NooDota said: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?

- #3

- 68

- 0

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

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