Решите систему уравнений 1/x-1/y = 1/12 5X-y = 18

1/x - 1/y = 1/12    (x ≠ 0; y ≠ 0)
5x - y = 18   

(y - x)/xy = 1/12
5x - y = 18

xy = 12(y - x)
5x - y = 18

xy = 12(y - x)
y = 5x - 18

x (5x - 18) = 12(5x - 18 - x)
5x^2 - 18x = 12(4x - 18)
5x^2 - 18x = 48x - 216
5x^2 - 18x - 48x + 216 = 0 
5x^2 - 66x + 216 = 0 
D = 4356 - 4320 = 36 = 6^2
x1 = ( 66 + 6)/10 = 7,2
x2 = ( 66 - 6 )/10 = 6 

x1 = 7,2
y1 = 5x1 - 18 = 18

x2 = 6
y2 = 5x2 - 18 = 12

Ответ
( 7,2 ; 18)
( 6; 12)