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SAT官方每日一题附答案和解析[数学](2014年11月18日)
日期:2014-11-19 09:11

(单词翻译:单击)

每日一题

Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

y = (-2x^2) + (bx) + 5

In the xy-plane, the graph of the equation above assumes its maximum value at x = 2. What is the value of b?


(A)-8
(B)-4
(C) 4
(D) 8
(E) 10

答案和解析

答案:D

解析:

Choice (D) is correct. Since the graph of the quadratic equation y = (-2x^2) + (bx) + 5 assumes its maximum at x = 2, it can be written in the form y = (-2 ((x-2)^2) + k, where k is some constant. This representation is equivalent to y = (-2x^2) + (8x)-8 + k, from which it follows that b = 8 (and-8 + k = 5).

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重点单词
  • equivalentadj. 等价的,相等的 n. 相等物
  • multipleadj. 许多,多种多样的 n. 倍数,并联
  • equationn. 相等,方程(式), 等式,均衡
  • graphn. 图表,示意图 vt. (以图表)表示 n.
  • constantadj. 经常的,不变的 n. 常数,恒量