Common Algebra Mistakes
Example: Function Notation 
The Goal
Evaluate f(x+h) for the function:
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
There are very few functions f(x) for which the equation f(x+h) = f(x) + h is true (it is true if y = f(x) is a straight line with slope 1).
Whatever we replace x with replaces x in the formula (even something silly like @):
Replace x with 4 to find f(4):
Note that 4 can be written as 3+1:
Following the pattern we can find f(3+h):
And f(x+h) is a matter of replacing the 3 by x:

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