2B=2(-4a的2次方+6ab+7)=-8a^2+12ab+14
A
=7a^2-7ab+2B
=7a^2-7ab-8a^2+12ab+14
=-a^2+5ab+14
|a+1|+(b-2)^2=0
|a+1|=0
(b-2)^2=0
a+1=0
a=-1
b-2=0
b=2
A=(-1)^2+5*(-1)*2+14=5