11:41

# 236. (★★) Σ の計算

7:52

Easy] Formulas for Sums of Equal Ratio Sequences [with exercises] that you will never forget.

15:28

# 235. (★★) スチュワートの定理

29:00

群論15 7の2019乗の下3桁の計算

13:05

# 248. (★★★)相加・相乗平均の関係

11:47

cos42°の値

13:17

The technique to solve this symmetrical equation in 30 seconds is too good to be true.

12:36

# 233. (★★★) Σ の計算