Question

几道数学题...谢谢呃、、、1.若x（y-1）-y（x-1）=4,求（x²+y²）/2 -xy的值.

Answer 1

1,(x²+y²）/2 -xy=1/2(x²+y²-2xy)=1/2(x-y)²由已知x（y-1）-y（x-1）=4可知xy-x-xy+y=4 y-x=4原题=82 ,由已知a+b=5,ab=3 可知 （a+ b）方=25即a方+b方+2ab=25可知a方+b方=19a³b-2a&su...