How Do You Solve a Calculus Limit Involving Negative Infinity?

[darklordavion]

Homework Statement

Limit: The square root of X^2-3X over 2X+1 as X is going towards negative infinity.

Homework Equations

The square root of X^2-3X over 2X+1 as X is going towards negative infinity.

The Attempt at a Solution

I tried to solve it but I have no idea what to do with the negative infinity part. I mean, if it was one number, I would just sub in that number and maybe factor, I am totally lost!

 

[Mark44]

Homework Statement

Limit: The square root of X^2-3X over 2X+1 as X is going towards negative infinity.

Homework Equations

The square root of X^2-3X over 2X+1 as X is going towards negative infinity.

The Attempt at a Solution

I tried to solve it but I have no idea what to do with the negative infinity part. I mean, if it was one number, I would just sub in that number and maybe factor, I am totally lost!

\sqrt{x^2 - 3x} = |x|\sqrt{1 - 3/x}
Does that help?

 

[darklordavion]

This: √X^2-3X
lim x→-∞ _________
Divided by 2X+1 Like that ^

 

[Mark44]

Yes, I understand what the problem is. I was suggesting something that might help you with it.

 

[flyingpig]

WHy can't you use L'Hospital's rule?

 

[darklordavion]

Yes, I understand what the problem is. I was suggesting something that might help you with it.

Oh sorry :( lol, I thought you interpreted it wrong.

I've tried just subing a random number, which was 4 and got 2/9... not sure what to do next.

 

[stonecoldgen]

multiply by the conjugate

it is like multiplying by 1, which is not ilegal, but it will cancel out things to you and make life easier

 

[darklordavion]

multiply by the conjugate

it is like multiplying by 1, which is not ilegal, but it will cancel out things to you and make life easier

can you show me?

 

[darklordavion]

Never mind, a friend who took BC cal last year helped me through AIM.

I got it :) Less work than needed too :)

 

[Mark44]

can you show me?

We are not here to do your work for you. Several people have suggested things to try. Pick one of the techniques and see what you get.

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