# What does [ ] define in math?

My teacher comes up with an expression saying:

an + (n+1)^{2} = 1/6[n(n + 1)(2n + 1) + 6(n + 1)^{2}]


I read on the internet that [ ] is used for a variaty of things. namingsly intervals, floor, etc. But in this situation what would they mean?

P.S an = n(n + 1)(2n + 1)/6

• It looks like your teacher is just using them as parentheses - in other words they have the same meaning as '(' and ')', but are used in their place to avoid confusion (since the 'round' parentheses have already been used once) Nov 4, 2016 at 12:43
• Is the right hand side of your equation supposed to be $\frac{1}{6[n(n+1)(2n+1) + 6(n+1)^{2}]}$ or just $\frac{1}{6}[n(n+1)(2n+1) + 6(n+1)^{2}]$? Parentheses are your friend! :) Nov 4, 2016 at 12:44
• The brackets are just serving as parentheses here, i.e. grouping terms. Nov 4, 2016 at 12:45
• ohh! i see your point user469444! Nov 4, 2016 at 12:49

Compare $$\frac16(n(n+1)(2n+1)+6(n+1)^2)$$ with $$\frac16\left[n(n+1)(2n+1)+6(n+1)^2\right]$$