1. Chapter 14 Formulae

2. Learning Objectives Write expressions in algebra Write expressions in algebra Write a formula Write a formula Know the difference between expressions & formula Know the difference between expressions & formula Substitute values into formulae and evaluate Substitute values into formulae and evaluate Substitute values into formulae with powers & roots Substitute values into formulae with powers & roots Re-arrange formulae Re-arrange formulae Solve problems by re-arranging formulae Solve problems by re-arranging formulae

3. Writing Expressions & Formulae An expression does not have an equal sign An expression does not have an equal sign A formula does have an equal sign A formula does have an equal signExamples 1. A box of matches has 55 matches, write an expression for the total matches in n boxes. 2. Write a formula for the total perimeter, P, of a shape with sides x – 3, x+ 2 & x

4. Substituting in Formula Examples 1. What is the value of A in the formula A = pq – r. when p = -1, q = 5 and r = -2 2. Find H when x = 5 and y = 7 in H = 3(3x – 2)

5. Formulae with Powers & Roots Examples 1. Find the value of S = (½p) 3, when (a) p = 4 (b) p = -4 2. Calculate √(5x) when x = 0.4 3. Use the formula v = √(u 2 + 2as) to find the value of v when a = -9.8, s = 1.67 and u = 45.3

6. Re-arranging Formulae Remember that when moving terms to the other side you do the opposite Remember that when moving terms to the other side you do the oppositeExamples 1. Make m the subject in k = 8m / 5 2. Make x the subject in y = 2x + 8 3. Make r the subject in A = 3r 2 4. Make b the subject in T = a + √b

7. More Re-arranging Examples 5. Make the bold letters the subject in the following: (a) 3a = 4b / 5 (b) 3(x – a) = x (c) e = ½mv 2 (d) a(b + x) = b(2a – x)

8. Solving Problems by Re-arranging 1. The volume of a cuboid, with length 7.8cm and breadth 5cm, is 136.5cm 3. Calculate the height of the cuboid. 2. V = 4 / 3 πr 3. Calculate r when the volume is 3.56×10 4.