Changing the subject of the formula a + b = c c is the subject Rearrange the formula to make b the subject so that The method is the same as solving equations b = ……... - a from both sides a + b = c -a -a b = c - a

Make b the subject a = bx + c rearrange so that b is on the right bx + c = a bx + c = a - c from both sides - c - c bx = a - c ÷ both sides by x ÷ x ÷ x bx = a - c b = a – c x

Make s the subject n = m - 3s add 3s to both sides n + 3s = m - n from both sides 3s = m - n s = m - n divide both sides by 3 3

Make r the subject reverse to get r on left multiply both sides by s p = q + r s q + r = p s reverse to get r on left multiply both sides by s q + r = sp r = sp – q - q from both sides

Make b the subject reverse to get b on left multiply out the bracket s = 3(a + b) reverse to get b on left 3(a + b) = s multiply out the bracket 3a + 3b = s - 3a from both sides 3b = s - 3a 3b = s - 3a 3 divide both sides by 3

The area of a trapezium is Find h (height) when A = 40 a = 10 b = 6 A = h(a + b) 2 Make h the subject then substitute in the values How?? 1st rearrange the formula 2 h(a + b) = A 2 h(a + b) = A x2 h(a + b) = 2A h(a + b) = 2A h = 2 Aa a + b divide by (a + b) substitute in the values A = 40, a = 10, b = 6 80 16 h = 2 x 40 = 10 + 6 = 5

Turn to page 117 Complete exercise 18.1A Then exercise 18.1B on page 118