$\underbrace{333......3}_{50}$ × $\underbrace{333......3}_{50}$
= $\underbrace{333......3}_{50}$ × 3 × $\underbrace{111......1}_{50}$
= $\underbrace{999......9}_{50}$ × $\underbrace{111.....1}_{50}$
= (1$\underbrace{00......0}_{50}$-1) × $\underbrace{111.......1}_{50}$
= $\underbrace{111......1}_{50}$$\underbrace{000......0}_{50}$- $\underbrace{111......1}_{50}$
= $\underbrace{111........1}_{49}$0$\underbrace{888......8}_{49}$9