<=> 12(x2 + y2) = 25xy
<=> 12(x - y)2 = xy
<=> \(\frac{\left(x-y\right)^2}{xy}\)= \(\frac{1}{12}\) (1)
ta có: \(\frac{x^2+y^2}{xy}\) = 25/12
<=> [(x + y)2 - 2xy]/xy = 25/12
<=> (x + y)2/xy - 2 = 25/12
<=> (x + y)2/xy = 49/12 (2)
chia (1) cho (2) đc:
(x + y)2/(x - y)2 = 49
<=> (x + y)/(x - y) = 7