Got it! Actung! The picture as usual is not correct!
On the picture not only triangles, but whole sectors must be in white!
In this case it has easy solution.
Area of shaded region = 100*Pi - 2*n/(2*Pi) = 100*Pi(1 - n/Pi) = 80*Pi.
Hence n = Pi/5, where n - third angle in triangle.
Hence a+b+c+d = (8*Pi)/5 = 288.
hi lime i am new to this forum
file:///F:/WINDOWS/TEMP/moz-screenshot.jpg
file:///F:/WINDOWS/TEMP/moz-screenshot-1.jpg:wacko: 2*n/(2*Pi)
how did you write that file:///F:/WINDOWS/TEMP/moz-screenshot-2.jpg
