1953 AMC 12 第 44 题

先试着解答 1953 AMC 12 第 44 题,然后核对你的答案与精心整理的解答,解答来自 LIVE by Po-Shen Loh。你也可以参加完整限时模拟考试、查看全部 1953 AMC 12 解答,或核对答案。

所有题目均经美国数学协会(MAA)官方合法授权使用。

44.

在解一道可化为二次方程的问题时,一名学生只把方程的常数项写错了,求得的根为 88 和 22。另一名学生只把一次项系数写错了,求得的根为 −9-9 和 −1-1。正确的方程是:
In solving a problem that reduces to a quadratic equation one student makes a mistake only in the constant term of the equation and obtains 88 and 22 for the roots. Another student makes a mistake only in the coefficient of the first degree term and finds −9-9 and −1-1 for the roots. The correct equation was:
x2−10x+9=0x^2-10x+9=0
x2+10x+9=0x^2+10x+9=0
x2−10x+16=0x^2-10x+16=0
x2−8x−9=0x^2-8x-9=0
以上答案均不正确
none of these
答案:A
知识点:quadratic rootsVieta formulascoefficients
小提示:
由根之和 8+28+2 可确定第一名学生方程中正确的一次项系数
The first student’s correct linear coefficient is determined by the sum 8+28+2
大提示:
由根之积 (−9)(−1)(-9)(-1) 可确定第二名学生方程中正确的常数项
The second student’s correct constant term is determined by the product (−9)(−1)(-9)(-1)
解答:
第一名学生只改错了常数项,所以正确的 xx 系数应与根为 88 和 22 的首一二次方程相同,即 −(8+2)=−10-(8+2)=-10。第二名学生只改错了这个一次项系数,所以正确的常数项为 (−9)(−1)=9(-9)(-1)=9。因此正确方程是 x2−10x+9=0。 x^2-10x+9=0\text{。}
因此,正确答案是 A。
The first student changed only the constant term, so the correct coefficient of xx is the one in the monic quadratic with roots 88 and 2:2: it is −(8+2)=−10.-(8+2)=-10. The second student changed only that linear coefficient, so the correct constant is (−9)(−1)=9.(-9)(-1)=9. Therefore the correct equation is x2−10x+9=0. x^2-10x+9=0.
Thus, the correct answer is A.
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