Question

已知a(a-1)-(a²-b)=2,求代数式ab-a²+b²／2的值

要过程，谢谢

Answer 1

a(a-1)-(a^2-b)=2
a^2-a-a^2+b=2
b-a=2

ab-(a^2+b^2)/2
=-1/2(a^2-2ab+b^2)
=-1/2(a-b)^2
=-1/2x4
=-2

Answer 2

a(a-1)-(a^2-b)=a^2-a-a^2+b=-a+b=2
a-b=-2

ab-(a^2+b^2）/2
=-(a^2-2ab+b^2)/2
=-(a-b)^2/2
=-4/2
=-2