1、(1)
(x+y)^2=x^2+2xy+y^2=(x^2+y^2)+2xy
所以:x^2+y^2=(x+y)^2-2xy=16-(-2)=18
(2)
(x-y)^2=x^2+y^2-2xy=18-(-2)=20
2、a^2=-3a-1
a^3=a·a^2=-3a^2-a=-3·(-3a-1)-a=8a+3
3a^3+(a^2+5)(a^2-1)-5(a+1)(a-1)-6a
=3·(8a+3)+(-3a+4)(-3a-2)-5a^2+5-6a
=18a+14+4a^2-6a
=4a^2+12a+14
=4·(-3a-1)+12a+14
=10
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