Question

若a(a+2)-(a的平方+2b)=10,则ab-（a的平方+b的平方）除以2的值.

Answer 1

a(a+2)-(a^2+2b)=10

a^2+2a-a^2-2b=10

2a-2b=10

a-b=5

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

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

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

= -1/2*25

= -12.5