霍恩规则计算求值多项式 P(x) = ∑k−0n\sum_{k-0}^n∑k−0naka_kakxkx^kxk 霍恩规则:P(x) = a0a_0a0 + x(a1a_1a1 + x(a1a_1a1 + x(a2a_2a2