先分解因式,再代入求值:(1)9X平方+12XY+4Y平方,其中X=3/4,Y=-1/2;(2)已知X+Y=1,求1/2X的平方+XY+1/2Y的平

601920119：
(1)9x²+12xy+4y²
=(3x)²+12xy+(2y)²
=(3x+2y)²
=[3×(3/4)+2×(-1/2)]²
=(9/4-1)²
=(5/4)²
=25/16
(2)1/2x²+xy+1/2y²
=1/2(x²+2xy+y²)
=1/2(x+y)²
=1/2×1
=1/2