rw [Finset.mem_range] at hi
i : ℕ
hi : i ∈ Finset.range 330
⊢ ↑((∏ x ∈ (Finset.range 330).erase i, (660 + x) * (1319 - x)) * ((660 + i) * (1319 - i))) /
      ((660 + ↑i) * (1319 - ↑i)) =
    ↑(∏ j ∈ (Finset.range 330).erase i, (660 + j) * (1319 - j))
i : ℕ
hi : i < 330
⊢ ↑((∏ x ∈ (Finset.range 330).erase i, (660 + x) * (1319 - x)) * ((660 + i) * (1319 - i))) /
      ((660 + ↑i) * (1319 - ↑i)) =
    ↑(∏ j ∈ (Finset.range 330).erase i, (660 + j) * (1319 - j))