## Christos 2 years ago 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

1. AravindG

Yep just use that formula

2. Christos

Check at my question

3. AravindG

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

4. AravindG

Can you write those?

5. julian25

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

6. Christos

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

7. AravindG

*f(x+h)

8. AravindG

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

9. Christos

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

10. Christos

thats what I said @AravindG

11. Christos

ah yea +**

12. AravindG

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

13. Christos

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)

14. AravindG

Why 0 ? You are told x=0 ?

15. Christos

lim (h--->0)

16. AravindG

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

17. AravindG

0+4x=4x

18. Christos

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

19. Christos

@AravindG

20. AravindG

so option 1 will be correct

21. Christos

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

22. AravindG

tell me which options you are speaking of

23. Christos

the red

24. AravindG

I see 4 options

25. AravindG

Which do you mean by saying both ?

26. Christos

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

27. AravindG

k

28. Christos

Forget it I got my mistake, jeez and phew

29. AravindG

lol Great you figured it out yourself :)