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# differentiation AS question watch

1. Stuck on question 3? Any help please
2. (Original post by poppydoodle)

Stuck on question 3? Any help please
What have you tried? The trickiest bit is the initial step I imagine, then the rest is as difficult as the earlier questions.
3. (Original post by Kevin De Bruyne)
What have you tried? The trickiest bit is the initial step I imagine, then the rest is as difficult as the earlier questions.
k(x+h) -kx
—————
h

is this right?
4. (Original post by poppydoodle)
k(x+h) -kx
—————
h

is this right?
Yes. Now you can simplify the numerator.
5. (Original post by Notnek)
Yes. Now you can simplify the numerator.
kx + kh- kx
——————
h

=

kx + k - kx

= k ???
6. (Original post by poppydoodle)
kx + kh- kx
——————
h

=

kx + k - kx

= k ???
Yes that's right. And k is a constant so the limit as h -> 0 is still going to be k.
7. Y=kx
So
Lim ((k(X+h)-kx)/h)= ((kx+Kh-kx)/h) =k

You can check the answer by differentiating it normally dy/dx= k
8. so if you have y = 8x then the gradient function is y = 8

in other words a constant gradient, which means it is a straight line graph.

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