Explanation:
x + y = 17
x = 17 - y
xy = 20
(17 - y)y = 20
-y² + 17y = 20
-y² + 17y - 20 = 0
the general solution to such a quadratic equation
ax² + bx + c = 0
is
x = (-b ± sqrt(b² - 4ac))/(2a)
in our case
y = (-17 ± sqrt(17² - 4×-1×-20))/(2×-1) =
= (-17 ± sqrt(289 - 80))/-2 =
= (-17 ± sqrt(209))/-2
y1 = (-17 + sqrt(209))/-2 = 1.271583853...
y2 = (-17 - sqrt(209))/-2 = 15.72841615...
the 2 numbers are
1.271583853...
15.72841615...