Question

solve:

(m+n)-1 (m-1+n-1) = (mn)-1

Answer 1

$(m + n) - 1(m - 1 + n - 1) = (mn) - 1 \\ (m + n) - m + 1 - n + 1 = (mn) - 1 \\ m - m + n - n + 1 + 1 = (mn) - 1 \\ 2 = (mn) - 1 \\ mn = 3$