Multiple Choice Question (MCQ)

If a>b and c>d , which of the following must be true?

  1. ×

    ac>bd

  2. ×

    a+b>c+d

  3. a+c>b+d

  4. ×

    a-b>c-d

  5. ×

    ad>bc

Collected in the board: Inequality

Steven Zheng posted 1 year ago

Answer

  1. ac>bd

    If a>b and c>d , the product of sides must not follow the order of size in original inequalities. Multiplying or dividing both sides by a negative number reverses the inequality.

    For example,

    4 > 3, -1 >-2, but 4\times(-1) > 3(-2), ture

    7 > 3, -1 >-2, but 7\times(-1) < 3(-2) , false

  2. a+b>c+d

    This statement is obviously false.

  3. a+c>b+d

    Addition of two inequalities of the same order will not change the order of the inequalities.

    If a>b and c>d

    Add the two inequalities, we get

    a+c>b+d

  4. a-b>c-d

    This statement is similar to B, which is Not true.

  5. ad>bc

    This statement is similar to A, which is also not true.

Steven Zheng posted 1 year ago

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