Research-based guidance and classroom activities for teachers of mathematics

The equals sign

The equals sign is a theme within quantities and algebraic expressions. Links to relevant activities and resources are on the right hand side of this page. 

The equals sign can be used to indicate: formulae such as A = ½ bh; equations such as x+y=5; identities such as 3a+3b=3(a+b); properties such as ‘vertically opposite angles are equal’ and functions such as
f(x) = 2x+3.

In school algebra the equals sign is usually used to indicate equality of value, such as 3+5=9-1, or angle ABC = angle ACB.

Typical misunderstandings about how to use the equals sign include:

  • Letters are objects to move around, e.g. ‘move x to the other side’
  • If there are letters in an expression you always have to find their value, so how can you find x in ‘5x+10=5(x+2)’?
  • The equals sign means ‘calculate’