Question

已知x乘(x减1)减(x的平方减y)等于负4,求(2分之x的平方加y的平方)减xy的值

Answer 1

x(x-1)-(x²-y)=-4

x²-x-x²+y=-4

y-x=-4

x-y=4

所以原式=(x²-2xy+y²)/2

=(x-y)²/2

=4²/2

=8