(2)a²-2a+3与-2a+3(3)3a与-a

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(2)a²-2a+3与-2a+3(3)3a与-a

(2)a²-2a+3与-2a+3(3)3a与-a
(2)a²-2a+3与-2a+3(3)3a与-a

(2)a²-2a+3与-2a+3(3)3a与-a
a²-2a+3-(-2a+3)
=a²-2a+3+2a-3
=a²≥0
所以 a²-2a+3≥-2a+3
3a-(-a)
=3a+a
=4a
a>0时
3a>-a
a=0时
3a=-a
a