How to check if derivative equation is correct? I can calculate the derivative of a function using the product rule, chain rule or quotient rule.
When I find the resulting derivative function however, I have no way to check if my answer is correct!
How can I check if the calculated derivative equation is correct? (ie I haven't made a mistake factorising, or with one of the rules).
I have a graphics calculator.
Thanks!

I have a TI-84, and it has a Numeric Derivative function. It can be found by pressing the MATH button, and it is the 8th function in the list. 
nDeriv( will appear on the screen. You then can enter in the original function, comma, the variable in the original function (probably $x$ unless you have something else stored), comma, and the value for x you wish for the calculator to plug in to the derivative. 
For instance, if I am finding the value of the derivative of $x^3-5x+9$ at $x=10$, my screen would show this before pressing enter: 
nDeriv(X^3-5X+9,X,10) 

You then plug in the same x value to your supposed derivative which you are checking and manually solve it. 
If the values match, your derivative is correct! 
