x / 3 = 5 / x + 2
x( x + 2) = 3·5
x² + 2x = 15
x² + 2x - 15 = 0, ec de gradul II
a = 1, b = 2, c = - 15
delta = b² - 4ac = 2² - 4·1· ( -15) = 4 + 60 = 64
delta = 64
x1 = ( - b - √delta) / 2a = ( - 2 - √64) / 2 = ( - 2 - 8) / 2 = - 10/2 = - 5
x1 = - 5
x2 = ( - b + √delta) / 2a = ( - 2 + √64) / 2 = ( - 2 + 8) / 2 = 6/2 = 3
x2 = 3
S = { - 5, 3}
