2(2a^2+9b)+3(-5a^2-4b)
=4a^2+18b-15a^2-12b
=6b-11a^2
1/4(-4x^2+2x-8)-(1/2x-1)
=-x^2+1/2x-2-1/2x+1
=-x^2-1
x=1/2 所以原式=-（1/2）^2-1=-5/4
2(2a^2b+ab^2)-2(a^2b-1)-2ab^2-2
=4a^2b+2ab^2-2a^2b+2-2ab^2-2
=2a^2b
a=-2,b=2 所以原式=16