Calculus I Problem...

[nikok]

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They give an answer of -6, but I get an answer of 6/0, therefore the limit does not exist.

They're answer:

What am I doing wrong?

 

[V5RED]

multiply the numerator and denominator by -1 and then you cancel out 9-x in the top and bottom and are left with -(sqtrx+3)=>-6

 

[nikok]

multiply the numerator and denominator by -1 and then you cancel out 9-x in the top and bottom and are left with -(sqtrx+3)=>-6

Gotchya, is there a way to know whether to substitute (like I did), or to multiply by -1?

Don't want to make this mistake on an exam...

 

[mauberley]

Gotchya, is there a way to know whether to substitute (like I did), or to multiply by -1?

Generally, limits are calculated because the formula, by itself, yields something that isn't a number. Simple substitution into the formula to get division by zero isn't the point of the exercise but rather to find out what the behavior is as you approach the value that yields the undefined value.

Also, ib4tl. SDN is not a place for help with homework.

 

[deleted393595]

They give an answer of -6, but I get an answer of 6/0, therefore the limit does not exist.

They're answer:

What am I doing wrong?

When you get 0/0 after you plug in your number into your original formula, you have to resort to L'Hopital's rule.

That being said, I second maub's post. Hw questions do not belong on this thread.

 

[I'm No Superman]

You could also do the derivative of the top and bottom, which would be -1/(.5(9)^-.5) which equals -6

Edit: damn, beat me to it.

 

[nikok]

Generally, limits are calculated because the formula, by itself, yields something that isn't a number. Simple substitution into the formula to get division by zero isn't the point of the exercise but rather to find out what the behavior is as you approach the value that yields the undefined value.

Also, ib4tl. SDN is not a place for help with homework.

When you get 0/0 after you plug in your number into your original formula, you have to resort to L'Hopital's rule.

That being said, I second maub's post. Hw questions do not belong on this thread.

Thanks, ill do some research on it. I'm doing practice problems and this one was driving me nuts, sorry.

 

[phonyreal98]

They give an answer of -6, but I get an answer of 6/0, therefore the limit does not exist.

They're answer:

What am I doing wrong?

Post a homework problem on SDN. 😛

 

[vin5cent0]

This post makes me so freakin happy to be done with calculus. Hallelujah

 

[gettheleadout]

This post makes me so freakin happy to be done with calculus. Hallelujah

Agreed!

But as Mauberley said, this is not a forum for homework help. Thread closed.