How to approach it?

Level pending

L = l i m n > 0 + ( s i n x ) 1 l n x {lim}_{n->{0}^{+}} {(sin x)}^{\frac{1}{ln x}}

Find [ L ] [L]

JFF - I used L to celebrate launch of Android 5.0 Lollipop :P


The answer is 2.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Assuming that the limit is as x 0 + x \rightarrow 0^{+} , then we first note that the limit is of the indeterminate form 0 0 0^{0} .

So we look instead at

ln ( L ) = ln ( lim x 0 + ( sin ( x ) ) 1 ln ( x ) ) = lim x 0 + ( ln ( ( sin ( x ) ) 1 ln ( x ) ) = lim x 0 + ln ( sin ( x ) ) ln ( x ) \ln(L) = \ln(\lim_{x \rightarrow 0^{+}} (\sin(x))^{\frac{1}{\ln(x)}}) = \lim_{x \rightarrow 0^{+}} (\ln((\sin(x))^{\frac{1}{\ln(x)}}) = \lim_{x \rightarrow 0^{+}} \dfrac{\ln(\sin(x))}{\ln(x)} .

Now apply L'Hopital's rule to this last expression to find that

ln ( L ) = lim x 0 + cos ( x ) sin ( x ) 1 x = lim x 0 + cos ( x ) sin ( x ) x = 1 1 = 1 \ln(L) = \lim_{x \rightarrow 0^{+}} \dfrac{\frac{\cos(x)}{\sin(x)}}{\frac{1}{x}} = \lim_{x \rightarrow 0^{+}} \dfrac{\cos(x)}{\frac{\sin(x)}{x}} = \dfrac{1}{1} = 1 ,

where I made use of the fact that lim x 0 sin ( x ) x = 1 \lim_{x \rightarrow 0} \frac{\sin(x)}{x} = 1 .

So since ln ( L ) \ln(L) goes to 1 1 as x 0 + x \rightarrow 0^{+} , we conclude that L L goes to e 1 = e = 2.71828..... e^{1} = e = 2.71828..... . Thus L = 2 \lfloor L \rfloor = \boxed{2} .

Yeah! Nice! Did the same!

Kartik Sharma - 6 years, 7 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...