若x+y=3,求½x²+xy+½y²的值.

若x+y=3,求½x²+xy+½y²的值.
若x+y=3,求½x²+xy+½y²的值.

若x+y=3,求½x²+xy+½y²的值.
½x²+xy+½y²
=½(x²+2xy+y²)
=½ (x+y)²
=½×3²
=½×9
=9/2
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