



 
Helen, As "h" is an indeterminate, not a number, it is unnecessary to specify that it doesn't equal 0. First find (and expand) f(x+h), that is, (x+h)^{2}  (x+h) +4. Now subtract x^{2} x + 4 (and simplify). Now divide by h (and simplify.) You will find that what you have after the last step will divide by h since f is a polynomial. When you get to calculus (which is what this is in preparation for!) you will learn how to use limits to deal with other functions. Good Hunting!
 


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