y' = 2 - 18/(x-8)²18/x-8这个要怎样导，过程？d[18/(x-8)]/dx = d[18/(x-8)]/d(x-8) · d(x-8)/dx = -18/(x-8)² · 1 = -18/(x-8)²因为d(ax^n) = nax^(n-1)d[18/(x-8)]/d(x-8) = d[18(x-8)^(-1)]/d(x-8) = -1x 18(x-8)^(-2) = -18/(x-8)²