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Where am I going wrong?

Find the difference quotient for: $f(x)=2-x-3x^2$

$$\frac{[ 2-(x+h)-3(x+h)^2 ] - [ 2-x-3x^2 ]}{h}$$




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up vote 3 down vote accepted

Well, nowhere. Everything is OK.

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But shouldn't the answer be -6x-1? – AFerrara May 30 '12 at 2:33
@AFerraro: That is when $h \to 0$ which happens to be the derivative :) – user9413 May 30 '12 at 2:33
Yes, but you need to take the limit, and what you have found is the quotient. To find the derivative you have to let $h \to 0$ – Pedro Tamaroff May 30 '12 at 2:34
@AFerrara It will be $-6x-1$ only when you take the limit as $h \rightarrow 0$. – user17762 May 30 '12 at 2:34
Ok, I thought they were the same, Thanks – AFerrara May 30 '12 at 2:35

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