Expressions and identities
An algebraic expression is not an equation, it is a combination of numbers, letters and operations. It also does not contain an equal sign.
4x + 6 + 5x – 3
An identity is an expression re-wrieen in a equivalent form.
4x + 5 + 2x – 2 ≡ 6x + 3
It can also be written with the ≡ or the = symbol.
An equation is an algebraic expression and a number, or two algebraic expressions with an equals sign. The equation also has a unknown which has a particular value, finding this value is also known as “solving” the equation.
x + 8 = 15
A formula take equations a step further by linking two or more physical variables.
P = 2(l + x)