Basics of trigonometric limits!

Calculus Level 2

lim x 0 sin ( 3 x ) + sin ( 2 x ) tan 3 x tan 2 x \lim _{ x\rightarrow 0 }{ \frac { \sin \left( 3x \right) +\sin \left( 2x \right) }{ \tan 3x-\tan 2x } }


The answer is 5.

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3 solutions

Noel Lo
May 7, 2015

As x x approaches 0, we have 3 x + 2 x 3 x 2 x = 3 + 2 3 2 = 5 \frac{3x+2x}{3x-2x} = \frac{3+2}{3-2} = \boxed{5} . Remember that for extremely small x x , both s i n x sin x and t a n x tan x approach x x .

Thushar Mn
Apr 18, 2015

this problem is very easy.. divide numerator and denominater by x.then use standard limits sin(nx) by x as x tends to zero..

Rohit Sachdeva
Apr 18, 2015

This is level 5...?

I just applied L-H rule once to get that..

The above limit can be written as:

d d x ( s i n 3 x + s i n 2 x ) d d x ( t a n 3 x t a n 2 x ) \frac{\frac{d}{dx}(sin3x+sin2x)}{\frac{d}{dx}(tan3x-tan2x)}

( 3 c o s 3 x + 2 c o s 2 x ) ( 3 s e c ² 3 x 2 s e c ² 2 x ) \frac{(3cos3x+2cos2x)}{(3sec²3x-2sec²2x)}

Which on applying limit x --> 0 gives (3+2)/(3-2) = 5

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