For the most part, expressions are entered using standard mathematical notation, with a few caveats:

• Multiplication is implied in expressions like:
  • 2x
  • cos(x)sin(x)
  • (x+1)(x-2)
  • ln(4)4^x
  • x|x+1|
  • x cos(x) (There must be a space between x and cos.)
• Closing parentheses are not optional (unlike, say, on TI-84 graphing calculators).
• All functions must have parentheses—for example, use sin(x) rather than sin x, and ln(|x|) rather than ln|x|.
• Exponentiation (like 7^x) can be entered as either 7^x or power(7,x).
• The inverse trig functions should be entered as atan, asin, and acos (and similarly for inverse hyperbolic trig).
• Absolute values can be entered as either |x| or abs(x).

I also have a page where you can practice integration (antiderivatives).

While I try to test this page fairly thoroughly, every time I change something, I run the risk of breaking something else. If you find it is misbehaving for you, please click THIS LINK to send me an email report of the problem.

For "skipped" functions, this page provides a link to wolframalpha.com where you can see the details of how to find the derivative (follow the link, then click "Show steps"). Note that this might fail for some functions, because some of my notation is tricky to translate to a form that WolframAlpha will understand.

To check if your answer is correct, the computer finds the exact derivative. If your function and the exact derivative have the same output value at 5 randomly selected x values between –8 and +8, it is judged to be the correct answer.

Because of this approach, a few (mostly) correct derivatives will be judged as wrong unless you enter them the "correct" way. For example, if you simplify the function sqrt(x²) to x, and enter the derivative as 1, it would (most of the time) be ruled incorrect. This is because sqrt(x²) = |x|, and the derivative of |x| is ±1 (specifically, +1 when x>0, and -1 when x<0). If you enter the derivative as abs(x)/x, or as x/sqrt(x^2), it will be counted as correct. I don't know of any other issues, but I have not tested this page to the point that I can guarantee it will never fail.