Question

已知a(a-1)-(a²-b)=5,求a²+b²/2-ab的值

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Answer 1

a(a-1)-(a²-b)=a^2-a-a^2+b=b-a=5
a²+b²/2-ab=(a^2-2ab+b^2)/2=(b-a)^2/2=25/2

Answer 2

a(a-1)-(a²-b)=5
a^2-a-a^2+b=5
a-b=-5
a²+b²/2-ab
=1/2(a^2-an+b^2)
=1/2(a-b)^2
=1/2*5^2
=25/2