The first formula is10 ∧ 5× (1+10× 5%) = x (1+9× 5%)+x (1+8× 5%)+

Because there is no compound interest, on the left is his total loan plus his principal 10 all interest.

On the right is the yuan he repays the loan every year. For example, in the first year, he has 654.38 million yuan, with 5% interest, and then he pays back X yuan, so this X yuan will not generate interest in the remaining 9 years, and so on. In the second year, X yuan will not generate interest for the remaining eight years, and will not generate interest for the last year. So on the right is the formula.

Ask me if you don't understand.