（a+2)2+|b-1/4|=0
a+2=0
a=-2

b-1/4=0
b=1/4

5a2b-[2a2b-(ab2-2a2b)-4]-2ab2
=5a2b-2a2b+ab2-2a2b+4-2ab2
=a2b-ab2+4
=ab(a-b)+4
=-2x1/4x(-2-1/4)+4
=9/8+4
=5.125