Derivative of -x using first principle

  • #1
35
3

Homework Statement


This is a silly question,but i have a problem.How do we solve derivative of -x using first principle of derivative. I know that if derivative of x w.r.t x is 1 then ofcourse that of -x should be -1. Also it can be solved by product rule taking derivative of -1.x .


Homework Equations




The Attempt at a Solution


Here is how i attempted it:
f(x)= -x
f(x+h)= -x+h
Using first principle :
dy/dx = [-x+h-(-x)]/h
= h/h
= 1
what is wrong here?please help. Thanks in advance:smile::redface:
 

Answers and Replies

  • #2
blue_leaf77
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f(x+h) = -x-h
 
  • #3
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3
f(x+h) = -x-h
But how does that work? Why it isn't -x+h ?:oldconfused:
 
  • #4
PeroK
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But how does that work? Why it isn't -x+h ?:oldconfused:

Try ##x = 0## and see what you get.
 
  • #5
35
3
Try ##x = 0## and see what you get.
Hey! I think i got it!
When, f(x)= x^2
f(x+h)= (x+h)^2
If, f(x)= -x
f(x+h)= -(x+h)
= -x-h
Is this right?
 
  • #6
Dick
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Hey! I think i got it!
When, f(x)= x^2
f(x+h)= (x+h)^2
If, f(x)= -x
f(x+h)= -(x+h)
= -x-h
Is this right?

Quite right.
 

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