Question

Derivatives,


There is this problem that asks me to find the derivative of f(x)=2x^2 ONLY by making use of this formula: f'(x)=lim(h-->0)(f(x+h)-f(x))/h


My Question is this:

http://screencast.com/t/fdJEOQduGCj

Answer 1

Yep just use that formula

Answer 2

Check at my question

Answer 3

f(x+h)=?
f(x)=?

Answer 4

Can you write those?

Answer 5

?????? it is right?????? the derivative is 4x

Answer 6

f(x)= 2x^2 f(x=h)= 2(x+h)^2

Answer 7

*f(x+h)

Answer 8

f(x+h)= 2x^2 f(x=h)= 2(x+h)^2

Answer 9

But my approach (the one with the red letters) gives 0. And I didn't do any mistake

Answer 10

thats what I said @AravindG

Answer 11

ah yea +**

Answer 12

What is your problem ? You are getting correct answer 4x ?

Answer 13

No, look. The black letters is the solution manual. On the other hand the RED letters are my approach. The solution gives 4x. My solution gives 0. Both solutions doesn't have any mathematical mistake. ( and it's driving me crazy)

Answer 14

Why 0 ? You are told x=0 ?

Answer 15

lim (h--->0)

Answer 16

that will be 0+4x .I dont see 0 anywhere

Answer 17

0+4x=4x

Answer 18

Do you see this http://screencast.com/t/YqaRwsAr5b

Answer 19

@AravindG

Answer 20

so option 1 will be correct

Answer 21

buth both options doesn't have any mathematical mistakes. Agree?

Answer 22

tell me which options you are speaking of

Answer 23

the red

Answer 24

I see 4 options

Answer 25

Which do you mean by saying both ?

Answer 26

Wait. Let me write the whole thing here on Open Study , 1 sec

Answer 27

k

Answer 28

Forget it I got my mistake, jeez and phew

Answer 29

lol Great you figured it out yourself :)