若M=(2x+3)(x-4),N=(x-7)(x+3)+8,则M与N的大小关系是( )A.M＞N

若M=(2x+3)(x-4),N=(x-7)(x+3)+8,则M与N的大小关系是( )

A.M＞N B.M＜N C.M=N D.M≤N

答案

解析：

两式作差：M-N=(2x+3)(x-4)-［(x-7)(x+3)+8］=2x²-5x-12-(x²-4x-13)

=x²-x+1=(x)²+＞0,

∴M＞N.

答案：

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