2015年SAT數學:數學選擇練習題

2015/04/13 瀏覽次數:6 收藏
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  2015年SAT測驗,勤於演習,控制數學答題方法,成就才有晉升空間,下面是小編為考生預備的SAT數學選取演習,願望能對眾人有所贊助!

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

  If x + y = 3 and x - y = 5 , then x 2- y 2 =____

  (A) 4

  (B) 8

  (C) 15

  (D) 16

  (E) 64

  The correct answer is C

  Explanation:

  Recall that x 2- y 2 can be factored as (x + y) (x -y) . Since x + y = 3 and x - y = 5 , their product, x 2 -y 2 , is (3) (5) , or 15 .

  Another method of solution is to solve the two equations x + y = 3 and x - y = 5 simultaneously to get x = 4 and y = -1 . Then x 2- y 2 is 4 2- (-1) 2 = 16 - 1 = 15 .