2. 外语
  3. If -7x5 and -3y4, what is the greatest possible value of(y-x)(x+y)?

If -7x5 and -3y4, what is the greatest possible value of(y-x)(x+y)?

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问题 If -7x5 and -3y4, what is the greatest possible value of(y-x)(x+y)?
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答案99
解析 The correct answer is 99. Because you are looking for the greatest value of(y- x)(x + y), your goal is to make x + y as big as possible and y- x as big as possible. Therefore, from the range of values given, choose x= 5 and y=4 to get x + y=9, and x= -7 and y=4 to get y-x=ll. The greatest value of(y-x)(x + y)is(9)(11)= 99.
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