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SAT数学多项式函数考点实例
A polynomial function P has zeros -3,3/2,and 8. Which of the following polynomial functions could define P?
多项式函数P存在 -3,3/2,8三个零点,则P的多项式函数是以下哪一个?
A. P(x)=-3(x-3/2)(x-8) B.P(x)=-(x-3)(x+3/2)(x+8) C. P(x)=(x+3)(3x-2)(x-8) D. P(x)=(x+3)(2x-3)(x-8)
答案:D
解析:Recall that if K is a zero of a polynomial function defined as y=f(x), then x-k is a factor of f.
要牢记,如果K是函数y=f(x)的零点,则x-k是函数f的一个因式
Since the polynomial function P has the zeros -3,3/2,and 8,it follows that (x-(-3)),(x-3/2),and (x-8) must be factors of P.
既然该多项式函数P有-3,3/2,8三个零点,则可得到(x-(-3)),(x-3/2), (x-8)都是P的因式。
Therefore, we can define P as P(x)=a(x+3)(x-3/2)(x-8), where a is a nonzero constant.
所以,我们可以定义函数P为P(x)=a(x+3)(x-3/2)(x-8), 其中a是非零常量。
A constant factor, such as a, does not affect the zeros of the polynomial function. In order to rewrite the equation with integral coeffecients, let a=2.
最后一步,用整数系数改写一下该方程。
If a=2, it follows that
P(x)=a(x+3)(x-3/2)(x-8)
=2(x+3)(x-3/2)(x-8)
=(x+3)(2x-3)(x-8).
so the polynomial that could define P is P(x)=(x+3)(2x-3)(x-8).
得到最终的可能结果之一为P(x)=(x+3)(2x-3)(x-8).
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