I found out one funny way to look at it. Taking the good old (a + b)².
(a+b)² = a² + 2ab + b²
Since 2.5 = 2 + 0.5
2.5² = (2+0.5)²
It follows the (a+b)² structure so now we can see it that way,
2² + 2x2x0.5 + 0.5² = 4 + 4 + 0.25 = 6.25
Now we can make it easier to find stuff like 7.8²
7² + 2x7x0.8 + 0.8² = 49 + 14x0.8 + 0.64
= 49 + 11.2 + 0.64 = 60.84
Anyway, I don’t know if it is useful but definitely fun to do. Thanks for those lessons, it’s been a while since I’ve done math. And I really enjoy it!
