7、m^2+m≠0
m(m+1)≠0
m≠0且m≠-1
m^2-m=2
m^2-m-2=0
(m+1)(m-2)=0
m=-1
或者m=2
结论:m=2
8、y=2x^2-(3m-4)x+10
=2(x-(3m-4)/4)^2+10-(3m-4)^2/8
对称轴x=(3m-4)/4的左侧为单调递减区间
(3m-4)/4>=5
3m-4>=20
3m>=24
m>=8
9、y=f(x)=-x^2+5
f(0)=5
f(x1)=f(x2)
x1+x2=0
f(x1+x2)=f(0)=5
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