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anonymous
 one year ago
Let f(x)=2x2+4x+6. Then according to the definition of derivative f′(−8) is the limit as x tends to 8 of the expression.....?
anonymous
 one year ago
Let f(x)=2x2+4x+6. Then according to the definition of derivative f′(−8) is the limit as x tends to 8 of the expression.....?

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zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3Oh hmm.. this is the other definition of the derivative ok.. lemme try to remember...

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3\[\large\rm \lim_{x\to a}\frac{f(x)f(a)}{xa}\]I believe it looks like that. You have a secant line between the points (x,f(x)) and (a,f(a)) and you let x approach a to get yoor tangent line.

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3\[\large\rm f(x)=2x^2+4x+6\]The derivative definition evaluated at a=8 looks like: \[\large\rm \lim_{x\to a}\frac{f(x)f(8)}{x8}\]So just plug in all the pieces! :)

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3\[\large\rm f(8)=?\]Do you know how to figure this out?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yeah i have the answer, it's 28 but every time i plug the expression in it says it's wrong

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3\[\large\rm \lim_{x\to a}\frac{\color{royalblue}{f(x)}\color{orangered}{f(8)}}{x8}=\lim_{x\to a}\frac{\color{royalblue}{2x^2+4x+6}(\color{orangered}{2(8)^2+4(8)+6})}{x(8)}\]Ya I guess maybe they want you to plug it in completely unsimplified like this? It's important to put brackets around your f(8) to show that it's being applied to every term over there.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0well there's an incorrect 2 placed somewhere in there but i changed it and it is still wrong

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3You still don't have the brackets around the orange like I mentioned.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0you're right! i thought i had put them in lol

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0thank you! it comes out as correct now!

zepdrix
 one year ago
Best ResponseYou've already chosen the best response.3wow that's a lot of brackets <.< lol there must be a better way to do that
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