Dumb question: What do brackets mean outside of matrices? Ex: [4+(9 - -x)]

From Dumbo: Is that a matrix?

If it is, how about containing the matrix to prevent it from spilling over or disintegrating or playing around or being scattered or being stolen or being messed up by non-Math people, or the brackets are just being there to perplex you?

and CR. math question, fill in the blanks with words to make a pun

the words:

addition, center, circumference, polyhedron, postulate, coincide, concentric, dimension, divide, rectangle, rhombus, secant, elliptical, factor, hypotenuse, subtract, multiply, plus, theorem.

heres the riddles:

A child's face will light up atdimensionof candy

"the mention"

I bought my mother a book andsecantit by parcel post

"sent"

A banana is sure to make an ______static.

"an...."

There are only two words in the list that begin with vowels: additition and elliptical.

I takeelliptical. "electrical" static.

While giving his report, the nervous student became nonplused

"nonplussed"

Thistheoremboard consists of three layers

"3 of 'em"

"Please, Rick, say yes. Won't youconcentric?

"concentrate"