1.[(a^2+b^2)^2-4a^2b^2]/(a^2-b^2)
=[a^4+2a^2b^2+b^4-4a^2b^2]/(a^2-b^2)
=(a^2-b^2)^2/(a^2-b^2)
=a^2-b^2
=9-1/4
2.因为|x+y+7|+(xy-5)^2=0,而|x+y+7|和(xy-5)^2都一定大于或等于0,所以
x+y+7=0
xy-5=0
可得：x+y=-7;xy=5
3x^2·y^3+3x^3·y^2
=3(xy)^2·(x+y)
=-525