<Dl> <Dd> x (n) = x (x + 1) (x + 2) ⋯ (x + n − 1) = (x + n − 1)! (x − 1)! . (\ displaystyle x ^ ((n)) = x (x + 1) (x + 2) \ cdots (x + n - 1) = (\ frac ((x + n - 1)!) ((x-1)!)).) </Dd> </Dl> <Dd> x (n) = x (x + 1) (x + 2) ⋯ (x + n − 1) = (x + n − 1)! (x − 1)! . (\ displaystyle x ^ ((n)) = x (x + 1) (x + 2) \ cdots (x + n - 1) = (\ frac ((x + n - 1)!) ((x-1)!)).) </Dd> <P> In quantum mechanics, angle brackets are also used as part of Dirac's formalism, bra--ket notation, to note vectors from the dual spaces of the bra ⟨ A (\ displaystyle \ left \ langle A \ right) and the ket B ⟩ (\ displaystyle \ left B \ right \ rangle). </P> <P> In statistical mechanics, angle brackets denote ensemble or time average . </P>

When do you use square brackets in math