Which Limit Law should I refer to in my solution?


by Abuda
Tags: limit, refer, solution
Abuda
Abuda is offline
#1
Aug19-11, 11:50 PM
P: 7
1. The problem statement, all variables and given/known data
Evaluate the limit below indicating the appropriate Limit Law(s) implemented.
[tex]\lim_{x\rightarrow 0.5}\frac{2x^2+5x-3}{6x^2-7x+2}[/itex]

2. The attempt at a solution

[tex]\lim_{x\rightarrow 0.5}\frac{2x^2+5x-3}{6x^2-7x+2}=\lim_{x\rightarrow 0.5}\frac{2(x-0.5)(x+3)}{6(x-0.5)(x-(2/3))}=\lim_{x\rightarrow 0.5}\frac{2(x+3)}{6(x-(2/3))}=-7[/itex]

So would I be required to state anything when I can out the (x-0.5) factor?
(PS, I'm doing Real Analysis and have learnt about proving limits from first principles but I'm now trying to learn about using shortcuts by referencing theorems.)
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ehild
ehild is offline
#2
Aug20-11, 12:42 AM
HW Helper
Thanks
P: 9,834
Quote Quote by Abuda View Post
1. The problem statement, all variables and given/known data
Evaluate the limit below indicating the appropriate Limit Law(s) implemented.
[tex]\lim_{x\rightarrow 0.5}\frac{2x^2+5x-3}{6x^2-7x+2}[/tex]

2. The attempt at a solution

[tex]\lim_{x\rightarrow 0.5}\frac{2x^2+5x-3}{6x^2-7x+2}=\lim_{x\rightarrow 0.5}\frac{2(x-0.5)(x+3)}{6(x-0.5)(x-(2/3))}=\lim_{x\rightarrow 0.5}\frac{2(x+3)}{6(x-(2/3))}=-7[/tex]

So would I be required to state anything when I can out the (x-0.5) factor?
(PS, I'm doing Real Analysis and have learnt about proving limits from first principles but I'm now trying to learn about using shortcuts by referencing theorems.)
Did you mean so? Do not mix tex and itex.

Say that x--->0.5 means that x tends to 0.5 but never equals to it, so x-0.5 can not equal to zero so you can divide with it. After that explain that the limit of a sum is the sum of the limits, limit of a product with a constant is also equal to the constant times the limit, and the limit of the fraction is equal to the limit of the numerator divided by the (non-zero) limit of the denominator .

ehild
Abuda
Abuda is offline
#3
Aug20-11, 12:49 AM
P: 7
Thank you very much for helping me and fixing up my latex skills. Your explanation about canceling sounds good to me and the other notes about the algebra of limits.
Alex


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