Expressions, equations, formulae
& identities
Can you explain what these key words mean?
Can you give an example for each one?
2a + 3b + c
is an expression
is an equation
is a formula
is an identity
Expression
An expression is made up of
numbers and symbols,
but expressions never have
an equals symbol or inequality signs.
Here’s some examples:
2a
3x + 2
5y2
6a2 + 7
is an expression
is an equation
is a formula
is an identity
2a + 3 = 21
is an expression
is an equation
is a formula
is an identity
Equation
An equation is made of two expressions
that are linked by an equals sign
Equations can be solved
– this means you can find out what
number the letter symbol stands for.
Here’s some examples:
2a = 6
3x + 2 = 29
5y2=45
2a2 = 18
is an expression
is an equation
is a formula
is an identity
2a2 + 18
is an expression
is an equation
is a formula
is an identity
2l + 2w = P
is an expression
is an equation
is a formula
is an identity
Formula
A formula is a short way of writing some sort of
rule, for example A=πr2 is the formula for the
area of a circle.
A formula is a type of equation, but the symbols
in a formula have set meanings,
for example in the formula 2l + 2w = P
l stands for length, w stands for width and P
stands for perimeter.
𝑎2 + 𝑏2 = 𝑐 2
is an expression
is an equation
is a formula
is an identity
𝑎2 + 𝑏2
is an expression
is an equation
is a formula
is an identity
𝑎2 + 42 = 52
is an expression
is an equation
is a formula
is an identity
2(a + 3) = 2a + 6
is an expression
is an equation
is a formula
is an identity
Identity
An identity is equation which is always true –
this means it works no matter what number the
letter stands for.
There is a special symbol for an identity, this is
sometimes used in place of the equals symbol.
2(a + 3) ≡ 2a + 6
2a + 3b = a + 2b + a + b
is an expression
is an equation
is a formula
is an identity
F = ma
is an expression
is an equation
is a formula
is an identity
2a + 3b = c
is an expression
is an equation
is a formula
is an identity
5(x - 4) ≡ 5x - 20
is an expression
is an equation
is a formula
is an identity
5(x - 4)
is an expression
is an equation
is a formula
is an identity
20(5 - x) = 100 - 20x
is an expression
is an equation
is a formula
is an identity
5(x - 4) = 20
is an expression
is an equation
is a formula
is an identity
Check up:
Can you explain what these key words mean?
Can you give an example for each one?
expression
equation
formula
identity