programming my language

Hi Asghar,

sin2u = sin3u is only true if u = 0. 

So then put u = 0 into the second expression

sin(0 + 30) = sin30 = 1/2

Let me know if you have any further questions!

Thank you do much lewis .but dont you think of any other way.
i mean is this the only possible way.

I disagree. There are infinitely more answers. For example, if you use u=(pi) , the equation also works, where both sides equal 0. All possible angles for u can be represented as the following, where k is an integer.:

     Radians -

u = 2πk

u= (π/5) + (2πk/5)

     Degrees -

u = 360°k

u= 36° + 72°k

Another example is u=π/5 , where both sides would equal approximately 0.951

What trigometry section is that sum from.

I don't think all the steps I used can be found on Khan Academy

Yes, that is the only possible solution. 

In order for sin2u = sin3u to be true, 2u = 3u must be true. This is only true if u = 0. 

I'm at algebra 1 functions level, Geometry circle highschool level, and I haven`t even started trigonometry yet, I'm thinking to stick to the geometry section finishing the https://www.khanacademy.org/math/geometry-home/cc-geometry-circles then the trigonometry then going back to algebra, I'm not going to do trigonometry in algebra and pre-calc not section not until I'm finished the geometry all content high school level and trigonometry and yet I don`t want to bore myself into putting myself of KA.