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

[ElectroNewby]

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

 

[KeepItSimpleStupid]

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

 

[ElectroNewby]

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 !!

 

[MrAl]

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.