x + x
(one "x" + one "x"; don't forget there is a 1 in front of the x!)

2a +3
(two time "a" plus 3)

2(6 +3)
(two times the sum of 6 +3)

b^2 -4ac
(b square minus 4 times the product of "a" by "c")

An algebraic expression consist in one or more terms separated by addition or subtraction

Letters can be alone or in a group with other letters, in upper or more often in lower case. They stand for real things and concepts like time, speed, weight etc.... They are also called variables because their value can assume different numbers.

Each term has a umber in front called numerical coefficient and includes the positive or negative sign.

If a term has no variable then it is called a constant (its value doen't change, it is set; a number is a number)

Although the terms can be written with any order, traditionally they are written in alphabetical order with higher exponents first (e.g. a^3 comes before a^2 and before a)