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9 Expressions and formulae

a
a
!e length of the red line is a units. Key words

c !e length of the blue line is c units. Make sure you learn and

c understand these key words:
What does 4a represent? in terms of
What does a + c represent? subject of the formula
What does ac represent? changing the subject
factorise
algebraic fraction

a a a a Here is a rectangle.
Which of these is a formula for the length of the perimeter?
c 2(4a + 2c) 4c + 8a

4a + 2c + 4a + 2c 4(2a + c)
Which of these is a formula for the area of the rectangle?

c 4a × 2c 2c × 4a
8ac 8ca

a a a a

Can you #nd expressions for the lengths of
each of the two black lines in this diagram?
c

c
a
c

a a Can you #nd an expression for the area of

this square?
a

a

In this unit you will transform algebraic expressions using the laws of indices and factorisation. You will
also add and subtract algebraic fractions as well as substituting into formulae and expressions.

84 9 Expressions and formulae