How do you write seventy three using four nines?

Answer 1

73 = |- (sqrt(9!))/9 -| + 9 - sqrt 9 [ceiling]
= |_ sqrt sqrt sqrt sqrt sqrt sqrt sqrt 139! _|
{the rounded-down 128th-root of 139!; since we can make 139 with four
nines, this gives us another way to make 73 with four nines}

Another option that you may find is simpler:Noting that 9 to the power zero equals 1, then:
73 = (9 x 9) - 9 + 9 0


= 81 - 9 + 1 = 73