(x-y)的二次方
=(x+y)的二次方-4xy
=5的二次方-4×6
=1
所以 x-y=±1
x的二次方-y的二次方
=(x+y)(x-y)
=5×1
=5
或
x的二次方-y的二次方
=(x+y)(x-y)
=5×(-1)
= -5