What is the value of sintheta for a solid angle?

[Planck const]

Look here:

http://imageshack.us/photo/my-images/545/thep2.jpg/

I didn't learn about solid angle :shy:

So.. I geuss sintheta Is h/r ? or sqrt(h^2-b^2/16)/r ? Am I right?

Thanks in advanced

 

[HallsofIvy]

There is no "solid angle" here- two intersecting line segments lie in a single plane. Neither of the formulas you give is correct. If you drop a perpendicular from the point (x, a/2, h) to the x-axis, its length will NOT be h, it will be sqrt(a^2/4+ h^2) so the sine of the angle will be sqrt(a^2/4+ y^2)/sqrt(x^2+ a^2/4+ h^2).

 

[Planck const]

Thank you very much!