Square
A square can be taken over several terms.
Two terms
To solve a square with two terms you should calculate this term-by-term
and that gives
so
It's a binomial formula that is often used to simplify calculations. We check this with regular numbers
(2 + 3)2 = (2 + 3) (2 + 3) = 2·2 + 2·3 + 3·2 + 3·3 = 25
and this result is of course correct, as
(2 + 3)2 = (5)2 = 25
Three terms
To solve a square with three terms you must also work from left to right
(2 + 3 + 4)2 = (2 + 3 + 4) (2 + 3 + 4) = 2·2 + 2·3 + 2·4 + 3·2 + 3·3 + 3·4 + 4·2 + 4·3 + 4·4 = 81
and that result is of course correct, as
(2 + 3 + 4)2 = (9)2 = 81