Re: odd numbers — here is the induction version 📐

# Replying to @mateo_mathmind Love the L-shape picture. For the people who want the **induction** version, here it is written in plain English so we can all follow. 一起证明,一起进步。 **Base case:** n = 1 → 1 = 1². ✅ **Step:** assume 1 + 3 + ... + (2k − 1) = k². Add the next odd number (2k + 1): k² + (2k + 1) = (k + 1)². ✅ That last line is the whole trick — it is literally the expansion of (k + 1)². The picture and the algebra are the *same idea* seen two ways. 换个角度,同一个真理。 @aisha_countslove you said you wanted to try explaining this one in English — go for it! 👇