Yours Truly answers: When we use the formula

to compute the difference quotient, the correct steps should look like this:

(1) If you have trouble understanding this part, see me immediately so that we can go over it together.

(2) This is where many mistakes occur. Observe the following:

The square of  a + h   is so important that I encourage you to memorize it. Or, you can always do it by multiplying   a + h   by itself.

(5) When we factor  h  out of  –h, we should still have  –1  left.


Here is another example.