x + y = 7
lg x + lg y = 1
x, y > 0
lg xy = 1
xy = 10
x = 7-y
(7 - y)y = 10
y² - 7y + 10 = 0
D = 49 - 40 = 9
y12 = (7 +- 3)/2 = 5 2
y1=5 x1=2
y2=2 x2=5
x + y = 7
lg x + lg y = 1
x, y > 0
lg xy = 1
xy = 10
x = 7-y
(7 - y)y = 10
y² - 7y + 10 = 0
D = 49 - 40 = 9
y12 = (7 +- 3)/2 = 5 2
y1=5 x1=2
y2=2 x2=5