a, Ta có
A= x(x+2)+y(y-2)-2xy +37
=x2+2x+y2-2y-2xy+37
=x2-2xy+y2+2(x-y)+37
=(x-y)2+2(x-y)+37
Vì x-y=7
=>(x-y)2+2(x-y)+37=72+14+37=100
KL
b, Ta có B=x2+4y2-2x+10+4xy-4y
=x2+4xy+4y2-2x-4y+10
=(x+2y)2-2(x+2y)+10
Vì x+2y=5
=>(x+2y)2-2(x+2y)+10=52-10+10=25
KL