Calculus 1 question about limits
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Calculus 1 question about limits

[From: ] [author: ] [Date: 12-09-11] [Hit: ]
Thank you so much in advance.-LHôpitals rule does apply, but as usual you dont need it.All you need to know is that limits distribute over basically everything,and that tan(x) = sin(x)/cos(x).Then limits distribute over multiplication.......
Limit of 3X/tanX as x approaches 0.

I said it was undefined because I ended up using the sandwich theorem to find the limit of XsinX as x approached 0 and I got 0 and the limit of X3XcosX is 0 (resulting in a limit of 0/0). However I am usually wrong (lol) so I was wondering if I could be shown the correct way to do it WITHOUT using l'hospital's rule (if it even applies)...I have not learned that yet :). Thank you so much in advance.

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L'Hôpital's rule does apply, but as usual you don't need it. All you need to know is that limits distribute over basically everything, the special limit
lim[x->0] sin(x)/x = lim[x->0] x/sin(x) = 1

and that tan(x) = sin(x)/cos(x).

3x / tan(x) = 3x / (sin(x) / cos(x)) = 3xcos(x) / sin(x) = (x/sin(x))(3cos(x))

Then limits distribute over multiplication. So
lim[x->0] 3x/tan(x) = (lim[x->0] x/sin(x))(lim[x->0] 3cos(x)) = 1 * 3cos(0) = 1 * 3 * 1 = 3

-
lim 3x/tanx
x->0

lim 3x/[sinx/cosx]
x->0

lim 3x/{[sin(x)/x]x/cosx]
x->0

lim sin(x)/x =1
x->0

lim 3x/{1*x/cosx]
x->0

lim 3cosx
x->0

as lim x->0 then

3cos(0) =3

the limit is 3

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limit (3x / tanx) = 0 / 0
x–>0


3x / tanx

3x cosx / sinx <<———— cos(0) = 1

3x / sinx <<———— limit (x–>0) [ sin(x) / x ] = 1


limit (3x / sinx) = 3 ★
x–>0
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