On 9/1/2013 1:42 PM, Jim Thompson wrote:
See attachment. My mind is in rut today. I can't solve it. Help ;-)

...Jim Thompson



Define E = R + D
Define F = W / X

From similar triangles: Z = R * (W / X) = RF

From Pythagorean theorem: R^2 = (X/2)^2 + (E - H)^2

R^2 = X^2/4 + E^2 - 2EH + H^2

Substituting E = RF

R^2 = (X^2)/4 + (R^2)*(F^2) - 2HRF + H**2

Rearranging terms:

R^2*(1 - F^2) + 2RFH - (X^2)/4 - H**2 = 0

Which is a simple quadratic equation in R.