1. 取A为原点,AB为首册+x的数轴仔腔. C的坐标为x.
C处来自A的污染指数: y1 = ka/x^2
C处来自B的污染指念芹衫数: y2 = kb/(18-x)^2
y = y1+y2 = ka/x^2 + kb/(18-x)^2
2. y' = -2ka/x^3 - [2kb/(18-x)^3]*(-1) = -2ka/x^3 + 2kb/(18-x)^3
a = 1, x = 6时y最小, 即y'=0
-2k*1/6^3 + 2kb/(18-6)^3 = 0
b = 8