a + b + c = 180 (suma unghiurilor unui Δ)
a/2 = b/3 = c/4
a/2 = c/4, adica 4a = 2c , a = c/2
b/3 = c/4, deci 4b = 3c, b = 3/4 c
c/2 + 3/4 c + c = 180
2c + 3c + 4c = 180 x 4 = 720
9c = 720
c = 720:9 = 80
b = 3/4 c = 3/4 x 80 = 60
a = c/2 = 80/2 = 40
c - a = 80 - 40 = 40