Question

已知x+y=3 xy=1 ,求下列各式的值：

① x²+y² ② x²-xy+y² ③ (x-y)²

Answer 1

x²+y²=(x+y)²-2xy=7

x²-xy+y² =(x+y)²-3xy=6
(x-y)²=(x+y)²-4xy=5

Answer 2

X+Y=3
XY=1
（x+y）2=9
X2+2XY+Y2=9
X2+Y2=9-2XY=7
X2-XY+Y2=7-1=6
以此类推

Answer 3

7 6 5

Answer 4

1.3^2-2=7
2.3^2-3=6
3.3^2-4=5