9x0 - 0x9 = 891 + 198 - 1089.
Read this in a book by Shalinka Devi in my teens.

She also has a great about about 1729 to blow the qubic theory. 1729 is the lowest number that is the sum of two cubes in TWO different ways.

10^3 + 9^3 = 12^3 + 1^3.