# Homework Help: Derivative of A Trigonometric Function

1. Feb 27, 2012

### Bashyboy

1. The problem statement, all variables and given/known data
Find the derivative of f(x) = 1/4 sin^2 2x

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
f'(x) =1/4(sin 2x)^2

f'(x) = 1/4*2(sin 2x)(cos 2x)

f'(x) = 1/4(sin 4x)

That is my answer to the problem, but the book has it as f'(x) = 1/2(sin 4x)
What did I do wrong?

2. Feb 27, 2012

### lanedance

you forgot the factor of 2 when you differentiate (sin(2x))

3. Feb 27, 2012

### Bashyboy

Oh, yes, thank you.

4. Feb 27, 2012

### Staff: Mentor

(Above) This is f(x), not f'(x).

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook
{"found_math": false, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0}