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how to solve this

$$\lim_{\frac{sin(a+x) - sin(a-x) }{x}}

x\Rightarrow0$$

math trigonometry
Guest Aug 25, 2014

Best Answer 

 #3
avatar+27035 
+5

sin(a+x) expansion

Alan  Aug 25, 2014
 #1
avatar+27035 
+5

Expand sin(a+x) as a series in x:  

sin(a+x) = sin(a) + x*cos(a) + higher order terms involving multiples of x.

 

Similarly:

sin(a-x) = sin(x) - x*cos(a) + higher order terms

 

Therefore, sin(a+x) - sin(a-x) = 2x*cos(a) + higher order terms

 

(sin(a+x) - sin(a-x))/x = 2cos(a) + higher order terms.

 

The higher order terms all contain multiples of x, so when x goes to zero, these go to zero and we are left with:

$$\lim_{x \rightarrow 0}\frac{\sin(a+x)-\sin(a-x)}{x}=2\cos(a)$$

Alan  Aug 25, 2014
 #2
avatar+93644 
0

I do not know this expansion Alan.  

Melody  Aug 25, 2014
 #3
avatar+27035 
+5
Best Answer

sin(a+x) expansion

Alan  Aug 25, 2014
 #4
avatar+93644 
0

Thanks Alan. 

Melody  Aug 25, 2014

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