Question

someone who's taking calculus.. can you help me?

Answer 1

yes i probably can-what is the question?

Answer 2

thanks! okay so in this link http://tutorial.math.lamar.edu/Classes/CalcI/LimitsAtInfinityI.aspx#Limit_LimAtInf_Ex1a look at example 4 and 5... why can't i use infinity to plug in for both examples? for some reason, in ex. 4 they plugged in infinity and in ex 5 plugged in a 0 to get the final answer 0...

Answer 3

ok looking

Answer 4

very easy. you have different powers. when you have different powers after you will just plug in infinity you still will no be able to predics which one grows faster and which one slower. it just will no give you solution. infiniti in a power of two devided by infinity in the power of four does not make any sence

Answer 5

there are rules how to evaluate expression to deal with powers

Answer 6

but in ex 5, why couldnt i plug in the infinity even though there were different powers?

Answer 7

again-when powers are different you dont know what is bigger and what is smaller. therefore you dont know if it goes to 0 or to infinity

Answer 8

you take out the thing with the highest power. then you plug in infinity. after this step only.

Answer 9

wait in ex 4 they didnt plug in infinity. they plugged in 0 though...

Answer 10

is it because in ex4 the x approaches infinity and negative infininty that you plug in an infinity in the final step (to get - or +infinity/5) and in ex5 the x only approached negative infinity that they plugged in a 0 to get 0/2=0?

Answer 11

I dont know what are you talking about. both examples are identical.

Answer 12

* i meant in ex 5 they didnt plug in infinity

Answer 13

all you have to do is to remember-when there are different powers-you take out varible with the highest one and then plug in infinities

Answer 14

they sure did. you just missed this step

Answer 15

1 over infinity in a power of 2=0
etc

Answer 16

that is why they got 0 over 2 in the end

Answer 17

oh... okay... then in ex 4 why didn't the infinity be simplified to 0? sorry i'm so confused...

Answer 18

oh! is it because you cancel out all the rational numbers?

Answer 19

and in ex 4, once you cancel out all the rational numbers, then all you get is -x^3/5 so infinity^3 would still be infinity.... and in ex 5, once you cancel out al the rational numbers, there's nothing left in the numerator so it's 0?

Answer 20

they also plugged it in. 4 over infinity=0 plus infinity in the power of 3=infinity
now we need to divide infinity by expression in the bottom. number over infinity-0, 0-5=-5. now we have to devide infinity by -5. we got -infinity

Answer 21

wow you are really very confused and mix everything up. lets start from the beggining. what points do you miss?

Answer 22

oh, so you understand what is going on there now?

Answer 23

wait.. i want to double check..

Answer 24

good. check and ask.

Answer 25

so first you simplify the equation with the usual dividing out biggest exponent ...

Answer 26

exactly. but you have to do it in one case-when you divide different powers by different powers. this is the only case

Answer 27

then, say you get [z^3 ((4/z)+z^3)]/[z^3((1/z^3)-5)] from the problem in ex 4. cancel out the z^3.

Answer 28

obviously

Answer 29

but the very idea is that then you get numbers divided by infinities which are obviously zeros

Answer 30

plug in infinity to the z's, they are essentially 0s..

Answer 31

so then you can deal with it simply

Answer 32

yes, sure. but do you understand why they are zeros?

Answer 33

because when you divide out the numbers by infinity, they become too small?

Answer 34

you dont. that is why you are so lost))) take calculator plz

Answer 35

now devide some number for very big number. lets say devide 5 by 10 000

Answer 36

now devide 5 by 100 000 and then by 1000000

Answer 37

see what is going on. every time you get number closer and closer to 0

Answer 38

ya.

Answer 39

so you need to get rid of powers, and bring what you can to numbers

Answer 40

then you can see it and manage it

Answer 41

did you get the idea?

Answer 42

i think so...

Answer 43

good. I am very lost with my exam so i will go back to it.

Answer 44

thanks for the help!

Answer 45

no prob i got some great help here too