Limit as x approaches 0.

1. Nov 8, 2011

JustinLiang

1. The problem statement, all variables and given/known data
http://www.prep101.com/files/Math100PracticeExam.pdf [Broken]

Question 1m

3. The attempt at a solution
I tried to do this by using
lim sinx/x = 1
x->0

Factoring out x^2 from each one and I get infinity.
Why does this method not work?

I even tried plugging in 0.001 in my calculator and I get infinity :S.

Last edited by a moderator: May 5, 2017
2. Nov 8, 2011

QuarkCharmer

Is that sin(2x^2), sin^2(2x), sin(2)x^2 ?

3. Nov 8, 2011

Dick

Or is it 3sin(2x^2-6x^2+4x^6)? The question isn't very grammatical. And however I rearrange it I still can't figure out how to pull 4/5 as a limit out.

4. Nov 8, 2011

JustinLiang

It is 3sin(2x^2), you get 4/5, this limit is INSANE :P

5. Nov 8, 2011

vela

Staff Emeritus
It helps to use the substitution u=x2 to get
$$\lim_{u \to 0}\frac{3 \sin 2u - 6u + 4u^3}{u^5}$$Then three applications of the Hospital rule gets you to a limit you can evaluate.

6. Nov 9, 2011

Dick

Ah, indeed it does.