Thread: calculating limit of rational function

I'm not sure what to do when I plug in "a" in a rational function if the numerator comes out as zero, here is the problem:

lim (x+2)/(x^3+8)
x--> -2

the answer in the back is 1/12, could someone help me see how to find this?

Thx!!!

The thing is you got a fraction here:



where if you put x = -2 in, both the top and the bottom are zero.

So what you do is you factorise the bottom, and you'll see that it has a factor of x+2. So divide top and bottom by x+2 and see what you're left with.

Originally Posted by Matt Westwood

The thing is you got a fraction here:



where if you put x = -2 in, both the top and the bottom are zero.

So what you do is you factorise the bottom, and you'll see that it has a factor of x+2. So divide top and bottom by x+2 and see what you're left with.

to piggy back on this excellent advice, think "sum of two cubes"

oh ok, I should have seen that, lol. thx!

(x+2)/(x^2+4)(x+2) = 1/12 x--> -2

Originally Posted by calcnewbie

oh ok, I should have seen that, lol. thx!

(x+2)/[(x^2 - 2x +4)(x+2)] = 1/12 x--> -2

see the correction above. somehow you got the right answer when you had the wrong factorization i don't see how, you must've mistyped