a-2b=5 ab=3则2ab-a方b=

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a-2b=5ab=3则2ab-a方b=a-2b=5ab=3则2ab-a方b=a-2b=5ab=3则2ab-a方b=a²-2ab-10b=a(a-2b)-10b=5a-10b=5(a-2b)=

a-2b=5 ab=3则2ab-a方b=
a-2b=5 ab=3则2ab-a方b=

a-2b=5 ab=3则2ab-a方b=
a²-2ab-10b=a(a-2b)-10b
=5a-10b
=5(a-2b)
=5×5
=25
ab+(a²+b²)/2=(a+b)²/2=3²/2=9/2.
4x²+4xy+2y²+6y+9=0
(4x²+4x+y²)+(y²+6y+9)=0
(2x+y)²+(y+3)²=0
y+3=0,y=-3
2x+y=0,x=3/2
x-y=3/2+3=9/2.