f(x) = 5x - 2
5x - 2 = 0
5x = 2 / : 5
x = 0,4
f(x) = -1/3x + 1
-1/3x + 1 = 0
-1/3x = -1 / * (-3)
x = 3
f(x) = 21 - 3/7x
21 - 3/7x = 0
-3/7x = -21 / * (-7/3)
x = 49
