x+y=4 xy=-3 求(x-y)的2次方

来源：学生作业学帮网编辑：学帮网时间：2024/05/30 11:47:35

解
(x-y)²
=(x²-2xy+y²+4xy)-4xy
=(x²+2xy+y²)-4xy
=(x+y)²-4xy
=4²-4×(-3)
=16+12
=28