(1)(a+b)=5 ab=3
(a+b)²=25=a²+2ab+b²=a²+2X3+b²所以a²+b²=19 a²-2ab+b²=19-2ab=13
(a-b)²=13 a-b=±√13
(2)a²-b²=(a+b)(a-b)=±√13 ...