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∵x=1时,值为3；x=-2时,值为4(代入代数式)
∴a+3-b=3
4a-6-b=4
解得a=10/3,b=-10/3
∴当x=3时
(10/3)x²+3x+10/3
=(10/3)×9+3×3+10/3
=30+9+10/3
=39+10/3
=127/3