Let me assume that you are very familiar with it, then all you need to do is find a number, r that will make the first digit number become zero by adding (or minus). For example, the x of the square of 56 can be 4 or 6. If we choose 4, 56 + 4 is 60 (or if we choose 6, 56 - 6 is 50).
Next, all you need to do is using this equation: (Y - x)*(Y + x) + r2. For the case that Y = 56, x = 4, then we have 52*60 + 16 = 3120 + 16 = 3136
In fact, the secret behind this tips is embedded in the equation itself, that is:
Y2 = Y2 - x2 + x2Y2 = (Y2 + Y*x - Y*x - x2) + x2
Y2 = (Y - x).(Y + x) + x2
Lastly, as Anthony Robbins said "repetition is the mother of skill", do practice this technique from time to time to sharpen your mind. That's all for today. More fascinating articles and sharing will be updated from time to time in Xaivier Blog. So, you are welcome to subscribe our feed, look at our sitemap or simply visit our Homepage.
Written by: Xaivier Chia