Posted by **Casey** on Thursday, January 12, 2012 at 9:31pm.

Estimate the instanteous rate of change f(x) = x/(x+5) at (-3, -3/2)

Could someone explain this question to me, this isn't exactly the same as polynomial functions >.<

- Precalculus -
**Damon**, Thursday, January 12, 2012 at 9:46pm
It just says estimate so do that. add a small amount, say .1 to x and see how much f(x) changes

then the rate of change is (f(-3+.1) - f(3) )/.1

[f(-2.9) - f(3) ] / .1

= [-1.38 - (-1.5)]/.1

= .12/.1

= 1.2

- Precalculus -
**Damon**, Thursday, January 12, 2012 at 9:49pm
Now if you knew calculus you would have said:

dy/dx = [(x+5)(1) - x(1) ] / (x+5)^2

= 5/(x+5)^2

at x = -3 that is

5/4 = 1.25 well not bad

- Precalculus -
**Casey**, Thursday, January 12, 2012 at 9:56pm
What did you with -3/2? You have not used it, why?

- Precalculus -
**Damon**, Friday, January 13, 2012 at 7:39am
Well, I used 1.5 instead of 3/2

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