00:01
Ok, so let's find the derivative of f of x equal to x over x plus 2 by using the definition and the standard rules for differentiation.
00:17
Well, by using the definition here we just need to compute limit as h goes to zero of f of x plus h minus f of x over h.
00:32
Ok, well, i need more space.
00:36
This one is equal to limit as h goes to zero of 1 over h multiplied by f of x plus h, this one is x plus h over x plus h plus 2 minus f of x which is x over x plus 2.
01:04
Perfect.
01:05
Ok, now let's compute this limit here.
01:12
How can we compute this limit? ok, i'm gonna rewrite this guy in a more convenient form.
01:21
So limit as h goes to zero of 1 over h and this one can be rewritten as the fraction with denominator x plus 2 multiplied by x plus h plus 2 and the numerator is gonna be x plus 2 multiplied by x plus h.
01:43
This one is x squared plus hx plus 2x, ok, plus 2x plus 2h minus this one multiplied by this one.
02:00
So minus x squared minus hx minus 2x.
02:06
Ok, now we can simplify.
02:08
We can get rid of 2x here, negative 2x here, hx here, negative hx here, negative x squared, x squared and we have 1 over h and 2h here.
02:27
So we can get rid of h here and we are left with limit as h goes to zero of 2 over x plus 2 multiplied by x plus h plus 2...