# calculus help

#### Wheatmaster

##### Diamond Member
argh i'm studying for finals and i totally forgot how to do limits.

lim x-> infinity
(5-x^2)/2x^2

i thought you just plug in infinity but that doesn't seem to work. i can't factor anything...

#### gnuel3

##### Senior member
i thik you split it like 5/2x^2 - x^2/2x^2, then you get the limit as -1/2...

#### TuxDave

##### Lifer
Originally posted by: gnuel3
i thik you split it like 5/2x^2 - x^2/2x^2, then you get the limit as -1/2...
ding ding ding.... I would've probably just multiplied the top and bottom by 1/x^2 but I guess it works out the same.

#### Siva

##### Diamond Member
It amazes me that I got a 5 on the AP test... I don't remember a single bit of this stuff.

#### SpecialEd

##### Platinum Member
you could also use L'hospital's rule:

if you plug in infty and get infty/infty, just take the derivative of the top and bottom and the limits are equal.

#### cw42

##### Diamond Member
o crap, i just did this stuff last semester... i dont remember any calc