What numbers multiply to get 3.5 and add to get 4

What numbers multiply to get 3.5 and add to get 4

1- First number is:1.29289321881

2-2nd number is  :2.70710678119

Solve for x:
x (4-x) = 3.5

3.5 = 7/2:
x (4-x) = 7/2

Expand out terms of the left hand side:
4 x-x^2 = 7/2

Multiply both sides by -1:
x^2-4 x = -7/2

Add 4 to both sides:
x^2-4 x+4 = 1/2

Write the left hand side as a square:
(x-2)^2 = 1/2

Take the square root of both sides:
x-2 = 1/sqrt(2) or x-2 = -1/sqrt(2)

Add 2 to both sides:
x = 2+1/sqrt(2) or x-2 = -1/sqrt(2)

Add 2 to both sides:
Answer: | 
| x = 2+1/sqrt(2) or x = 2-1/sqrt(2)

Here is what you describe:

y x z = 3.5   and  y + z = 4

From the SECOND equation: y = 4 - z     Substitute that into the FIRST equation:  (4-z) x z =3.5

4z - z^2 = 3.5

z^2 - 4z + 3.5 = 0

Using quadratic equation results in z =~1.29289    so y = 4-z =~ 2.70721