- #1

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I know how to figure this out using a graphing calculator and using the 'short-cut' (nx^n-1), but I can't do it using limits. Help!

I'd like to use the equation lim x->a = f(x) - f(a) / x - a

Thanks!

- Thread starter fiziksfun
- Start date

- #1

- 78

- 0

I know how to figure this out using a graphing calculator and using the 'short-cut' (nx^n-1), but I can't do it using limits. Help!

I'd like to use the equation lim x->a = f(x) - f(a) / x - a

Thanks!

- #2

- 1,707

- 5

why would you do it like that? one yields the other. just use the "shortcut"

- #3

HallsofIvy

Science Advisor

Homework Helper

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However, since you ask, it's not particularly difficult: f(x)= x^2- 3x and f(a)= a^2- 3a.

f(x)- f(a)= x^2- 3x- a^2+ 3a= (x^2- a^2)- (3x-3a)= (x-a)(x+a)- 3(x-a). Now, when you divide that by x-a, what do you get? What is the limit of that as x goes to a?

I assume you know that "tangent line horizontal" means that the derivative must be 0.

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