Math  Please Help
posted by Barb .
Solve the system xy = 1, x + y =a
by using the identity
(x  y/2)^2 = (x + y/2)^2  xy

mmmh, can't quite see how that helps
I would just do:
y = 1/x
sub into 2nd
x + 1/x = a
x^2 + 1 = ax
x^2  ax + 1 = 0
x = (a ± √(a^2  4) )/2
y = 2/(a ± √(a^2  4) )