Expressions, Identities, Formulae, Equations
The following slides show examples of many common and sometimes
important expressions, identities, formulae and equations.
They are intended to provide stimulus for discussion. All students
should recognise some of the examples and be extended by others.
Students will be challenged to classify examples that are previously
unknown and should be encouraged to tackle these just as with the
examples that they do recognise.
Expressions, Identities, Formulae, Equations
An expression…
Is an algebraic statement consisting of at least one variable and one
number. It has no equals sign and so cannot be solved.
An equation…
Is an algebraic statement consisting of an expression and a variable (or
another expression) separated by an equal symbol. It can be solved to
find the particular values of the variable for which it is true.
A formula…
Relates one variable (letter) to another. It consists of one variable and an
expression separated by an equal symbol.
An identity…
Is an equation that is always true for any variables (letter values) you
choose.
8y  4
2x  1
i
sin x  0.5
5x  7  22
e 1  0
2a  3b
3(b  1)  27
2k 2  72
x 2  6 x  12
4a  6  2a  14
x  81
4(2a  )  5(3a  7)
7
2
4
1
2
x 5
e
x
2
sin 45 
2
2(3a  4)  6a  8
x x  x
a
b
a b
c  2r
a 2  b2  c 2
v  u  at
a 2  b 2  c 2  2bcCosA
 b  b  4ac
1  3a  4  2a  5  a x 
2a
2
V  IR
e  mc
F  ma
 xi
x
n
2
a0  a
a 1  a
y  mx  c
x0  1