QR 2sin(Pie+x)

[299678]

---

Members don't see this ad.

anyone knows why 2sin(pie+x) = -2sinx ?

 

[SaSSyBruin]

thats a simple Identity my man.... sin (-A) = - sin A

 

[Moabmad]

anyone knows why 2sin(pie+x) = -2sinx ?

Its because of the sinusoid wave form. A sine wave has a wavelength of 2PI. Half the wave length (PI) results in the same number of opposite sign. Remember that inside the () is an angle x... by adding Pi to that angle it just shifts on the graph Pi radians or degrees. Assume x is PI/2... then add PI = 3PI/2... which is equal in magnitude but opposite in sign as the sine of PI/2..... Check out the graph of a sine function in wiki and it will all make sense... sorry my explanation sucks.

http://en.wikipedia.org/wiki/File:Sine_and_Cosine.svg

 

[299678]

Thanks I I learned it long long times ago

 

[Streetwolf]

anyone knows why 2sin(pie+x) = -2sinx ?

sin(x+y) = sin(x)cos👍 + sin👍cos(x)

Thus (ignore the 2 for now):

sin(pi + x) = sin(pi)cos(x) + sin(x)cos(pi)
= 0 + (-sin(x))

Remember to put the 2 back in:

= -2sin(x)

 

[SaSSyBruin]

Hey streetwolf.. do you need to go to that whole calculation or would the identity be enough as I stated above since pi simply keeps the x value the same...

 

[Streetwolf]

Hey streetwolf.. do you need to go to that whole calculation or would the identity be enough as I stated above since pi simply keeps the x value the same...

You might know it for pi but what if the question asked for pi/2 instead? Or pi/4?

That formula would come in handy then.

Knowing what pi does in this case would be good enough since it's a fairly straightforward problem.