2. 外语
  3. DOne way to approach this question is to plug in values for one of the variables and determine the corresponding value for the o

DOne way to approach this question is to plug in values for one of the variables and determine the corresponding value for the o

admin2014-08-12  31
问题
选项
答案D
解析 One way to approach this question is to plug in values for one of the variables and determine the corresponding value for the other variable.
    One way to plug in: Plug in easy values. For example, you can plug in x = 0 and find that the corresponding value of y is -1; then you can plug in y = 0 and find that the corresponding value of x is -1. Since in the first case x is greater than y and in the second case y is greater than x, the correct answer is Choice D, the relationship cannot be determined from the information given.
    A second way to plug in: If you prefer to always plug in values of x to determine corresponding values of y, you can begin by writing the equation x +y = -1 asy = -x - 1. Writing it in this form makes it easier to find the corresponding values of y.
    You can start by plugging in the value x = 0. For this value of x, the corresponding value of y is y = -1, and therefore, x is greater than y. If you continue plugging in a variety of values of x, some negative and some positive, you will see that sometimes x is greater than y and sometimes y is greater than x.
    If you inspect the equation y = —x - 1, you can conclude that since there is a negative sign in front of the x but not in front of the y, for each value of x that is greater than 0, the corresponding value of y is less than 0; therefore, for each x > 0, x is greater than y.
    What about negative values of x? A quick inspection of the equation y = —x - 1 allows you to conclude that if x < -1, then y > 0, so y is greater than x.
    So for some values of x and y that satisfy the equation, x is greater than y; and for other values, y is greater than x. Therefore, the relationship between the two quantities x and y cannot be determined from the information given, and the correct answer is Choice D.
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