Question

Solve the simultaneous equations
xy = 4
x + y = 5

Answer 1

x = ⁴/_y                     
⁴/_y + y = 5
4 + y² = 5y               
y² − 5y + 4 =0
y² − y − 4y + 4 = 0
y(y−1) − 4(y −1) = 0
(y − 4)(y−1) = 0
y = 4 ; y = 1              
x = 1   x = 4