The Goal

Simplify the rational expression:

The Mistake

Find the algebra mistake:

(Roll the mouse over the algebra to see a hint in red)

The Correction

(Roll the mouse over the area above to see the correction in blue)

An Explanation

Any quantity to be canceled must be a common factor of the entire numerator and the entire denominator. Factor the h out in the numerator first, then cancel.
(For the equality to hold, the canceled factor must also be nonzero.)