maths~~~~~~~

其中一個為 x
另一個 = 4 - x
x^2 + (4 - x)^2 = 8.5
2x^2 - 8x + 16 = 8.5
2x^2 - 8x + 7.5 = 0
4x^2 - 16x + 15 = 0
(2x - 5)(2x - 3) = 0
x = 5/2 or x = 3/2
兩個數 5/2, 3/2

設兩個數為X,Y
(1)...X+Y=4
(2)...X^2+Y^2=8.5
(1),
X+Y=4
X=4-Y...(3)
(3)代入(2),
(4-Y)^2+Y^2=8.5
16-8Y+Y^2+Y^2=17/2
2Y^2-8Y+16=17/2
4Y^2-16Y+32=17
4Y^2-16Y+15=0
(2Y-3)(2Y-5)=0
Y=3/2 or 5/2
(Y=3/2)代入(3),
X=4-Y
X=4-3/2
X=5/2
(Y=5/2)代入(3),
X=4-Y
X=4-5/2
X=3/2
所以,
那兩個數=3/2 & 5/2

這兩數分別為(2.5, 1.5) or (1.5, 2.5)

假設這兩數為x and y

x+y=4
x^2+y^2=8.5

解這一個方程組就ga la