tobytoby1995

Could anyone help in these questions

ON LIMITS?

tobytoby1995

Besides, what is the meaning of negative infinity??

kiyiptsang

引用:

原帖由 tobytoby1995 於 2011-4-22 09:46 PM 發表
Besides, what is the meaning of negative infinity??

姐係負數的無極

E.g.    lim (x-> infinity )   -x

咁就會 -infinity

所以就會負數既無極

tobytoby1995

Thx!

小肥羊杰仔

1. 0
sinMX最大都只係1
個無限大...SO=0

小肥羊杰仔

3. 12+81-12=81

小肥羊杰仔

第2題
我唔識點講....
ANS=0

0310672

1) 0 BY SANDWICH THEOREM

blazehaze

1. 用 sinx/x 個條野

小肥羊杰仔

果個係X->0先用到

kiwakwok

For the first equation, use the sandwich theorem.
Note that -1/x ≤ sin(mx) / x ≤ 1/x, for x -> inf, both -1/x and 1/x converge to 0.

kiyiptsang

2)        5^x    乘 125     /   5.咩咩咩 ^x 乘  5^1/2

5^x  乘 5^(5/2)   /  5.咩咩咩^ x
因為5.咩咩咩 > 5
所以當x 係無限既話
就會 = 0

H2SO4

點解第一題唔可以上下乘 m???
(sin mx)/x
= (m sin mx)/mx
limit = m

桃子

引用:

原帖由 H2SO4 於 2011-4-22 11:35 PM 發表
點解第一題唔可以上下乘 m???
(sin mx)/x
= (m sin mx)/mx
limit = m

The question is asking for the limit as x->infinity, not x->0.

kiwakwok

What you have used is lim[x -> 0] sin x / x = 1.
It is not true for x -> inf