## jacobian 2 years ago compute the following integral

1. jacobian

|dw:1360696905475:dw|

2. ZeHanz

Do you mean:$\int\limits_{k+\Delta k}^{k-\Delta k}A \cos(kx) dk$In that case: A and x are considered to be constants, so you get:$\left[ \frac{ A }{ x }\sin(kx) \right]_{k-\Delta k}^{k+\Delta k}$Now subtitute values for k and subtract. On the other hand: shouldn't different variable names be used for the boundaries?

3. jacobian

i have it but the y are saying the final answer is |dw:1360697434010:dw|

4. ZeHanz

OK, let's try it:$\frac{ A }{ x }(\sin((k+\Delta k)x)-\sin((k-\Delta k)x)$ To get further, you need to remember the formula of Simpson for the difference of two sine functions: sin(a)-sin(b)=2cos((a+b)/2)sin((a-b)/2), but I have not (yet) got that answer of yours...

5. jacobian

@experimentX ,@ZeHanz ,@phi help me pls

6. experimentX

$\frac{2A \Delta k x \cos( kx) }{x} = 2A \Delta k \cos (kx)$

7. jacobian

by further simplifying i got this |dw:1360699433822:dw|

8. experimentX

|dw:1360699738616:dw|

9. jacobian

thanx for trying maybe they have made the mistake

10. experimentX

i have class at 7 in the morning ... sorry ... i gotta sleep now!!

11. jacobian

ok bye