a^2+b=-2,
a^2-b=4
等式两边分别相加,得
2a^2=2
a^2=1
5a^2-[3a^2+(5a^2-6a)-2(a^2-3a)]
=5a^2-(3a^2+5a^2-6a-2a^2+6a)
=5a^2-(6a^2)
=-a^2
= -1再问您几个题目：已知2y^2-4y-1=0,求4y^4-8y^3-4y^2+4y+3的值