How can I solve a one-sided limit without using l'Hopital's rule?

squirrelschaser
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Homework Statement

Find the ## lim _{x-> -1+} sqrt(x^2-3x)-2/|x+1| ##

Homework Equations

The Attempt at a Solution



I can only solve it using l'hopital rule and would like to know the steps of solving it without using it.

## lim _{x->-1+} (2x-3)/|1|= -5/4 ##
 
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squirrelschaser said:

Homework Statement

Find the ## lim _{x-> -1+} sqrt(x^2-3x)-2/|x+1| ##

Homework Equations

The Attempt at a Solution



I can only solve it using l'hopital rule and would like to know the steps of solving it without using it.

## lim _{x->-1+} (2x-3)/|1|= -5/4 ##
Multiply the expression by 1 in the form of the conjugate of the numerator over itself. The |x + 1| factor in the denominator can be replaced by x + 1, since x is to the right of -1, so x + 1 > 0. If the limit had been as x approaches -1 from the left you have to replace |x + 1| by -(x + 1).
 
squirrelschaser said:

Homework Statement

Find the ## lim _{x-> -1+} sqrt(x^2-3x)-2/|x+1| ##

Homework Equations

The Attempt at a Solution



I can only solve it using l'hopital rule and would like to know the steps of solving it without using it.

## lim _{x->-1+} (2x-3)/|1|= -5/4 ##

I suppose you mean$$
\lim_{x\to -1^+}\frac{\sqrt{x^2-3x}-2}{|x+1|}$$which is not what you wrote. Anyway since ##x>-1## you can write ##|x+1|=x+1##. Try rationalizing the numerator and see if you can get it then.

[Edit] Mark44 must type faster than I do.
 
Last edited:
I'm dumb. Much thanks.
 
No, you are careless- that, at least, is curable!
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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