This is part of a find the electric field problem. I've narrowed down the part I find confusing.
Consider a right triangle, with legs of length x and R. Angle θ is opposite x. Leg x is a segment of a ray starting where lines x and R intersect. There is a differential length dx along line x (it is at a vertex of the right triangle). Find dx in terms of R and θ.
standard trig functions, pythagorean theorem?
The Attempt at a Solution
The answer according to the solutions manual is dx = (R/cos^2 θ) dθ. Obviously, I cannot understand at all where that came from.
I did get R tan ( θ + dθ) = x + dx but that isn't very helpful either