h1 + b1 = h2 + b2 = h3 + b3,h1 = b2 + b3,h3 = (h1 + h2 + h3)*2/5联立以上四个方程，可以解出b1 = 1/4 (4 h2 - h3), b2 = -h2 + (5 h3)/4, b3 = h3/4, h1 = -h2 + ( 3 h3)/2再计算出 (b1+b2+b3) / (b1+b2+b3+h1+h2+h3) = 1/3
