# Will someone please walk me through how to do this problem?

If f(x) = 3x + 9, find {f(a+h) - f(a)} / h

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### 3 Answers

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- Jeff AaronLv 71 month agoFavourite answer
= ((3(a + h) + 9) - (3a + 9)) / h

= (3a + 3h + 9 - 3a - 9) / h

= 3h/h

= 3

= f'(x)

Note that h can't equal zero, but h can (and presumably does) approach zero.

- no sea naboLv 61 month ago
If f(x) = 3x + 9, find {f(a+h) - f(a)} / h

when h→0

then

{f(a+h) - f(a)} / h = f ' (a) definition of "derivate"

- ted sLv 71 month ago
do what it says by replacing x with the symbols " a + h " and also just " a " and then doing the algebra to simplify the quotient....not difficult if you KNOW algebra

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