d/dx(-4.9x^2+14.7x) | x=2 (I get -19.6 m/s instead of -4.9)

E

ElectroNewby

Member

• Sep 8, 2014

• #1

I'm having a hard time figuring this because it seems like I followed every step correctly.
I get to -4.9 with my calculator

Edit: not so correctly... see my 2nd post

 

Last edited: Sep 8, 2014

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Sep 8, 2014

• #2

I get 4.9 too; 2*-4.9+14.7 ; I haven't done it the hard way in quite a while.

 

E

ElectroNewby

Member

• Sep 8, 2014

• #3

Somebody pointed me my error :

I forgot to add the (x+dx) when replacing t (for y2) in the 14,7t part

Sorry for bothering for nothing !!

 

M

MrAl

Well-Known Member

Most Helpful Member

• Sep 9, 2014

• #4

Hello,

The derivative is 14.7-9.8*x, evaluated at x=2 we get -4.9 that's all there is to it.
There's no 't' in your original equation.