1 = 0,9(recurring)

proof:

let x be equal to 0,9 (recurring)
10x = 9,9 (recurring)
10x - x = 9x = 9,9 (recurring) - 0,9 (recurring) = 9
9x = 9
x = 1
0,9 (recurring) = x = 1
0,9 (recurring) = 1