Foundation and Higher · algebra vocabulary

Expression,
equation, formula
or identity?

one glance
tells you which

look for one thing first —

= or no =

no equals sign: an expression

then ask when it is true

card 1 of 6

Term

3x + 5

One part of an expression: a number, a letter, or both multiplied.

terms are separated by + and −

card 2 of 6

Expression

3x + 5

Terms added or subtracted, with no equals sign.

you can simplify it, not solve it

card 3 of 6

Equation

3x + 5 = 11

Two things that are equal. True for certain values only.

solve it: here x = 2

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Formula

A = l × w

A rule linking real quantities. Substitute to use it.

area, speed, volume…

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Identity

2(x + 3) ≡ 2x + 6

True for every value of the letter. Uses the ≡ sign.

both sides are the same thing

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Inequality

3x + 5 > 11

Two things that are not equal: one side is bigger.

the answer is a range of values

which one is it? —

No = sign

an expression

= for some values

an equation: solve it

≡ for all values

an identity

A formula is an equation
about real quantities.

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