(a+b)的二次方=a²+2ab+b²=16,①(a-b)的二次方=a²-2ab+b²=8 ②由①-②得4ab=8 ab=2应该是3(a-2b)(a/3+2/3b)=（a-2b）（a+2b）=a²-4b²不懂的再追问，
a+b=4a-b=2根号2a+b=-4a-b=-2根号2a+b=4a-b=-2根号2a+b=-4a-b=2根号2解这四组方程 就行了
