8 ms·

That's a neat visualisation. n^2 = sum(1..n) - sum(1..n-1) = 2sum(1..n-1) + n => n^2 - n = 2sum(1..n-1) => n(n-1) = 2*sum(1..n-1) => sum(1..n-1) = n(n-1)/

That's a neat visualisation. n^2 = sum(1..n) - sum(1..n-1) = 2sum(1..n-1) + n => n^2 - n = 2sum(1..n-1) => n(n-1) = 2*sum(1..n-1) => sum(1..n-1) = n(n-1)/2 And you can rewrite that as... sum(1..n) = n(n+1)/2

nhebb 9y ago
That's it! Makes me realize how rusty at math I've gotten. :/