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This chapter teaches how to write expressions and formulas in algebra, substitute values, evaluate equations with powers and roots, and rearrange formulas. It also provides examples and exercises to help students practice these skills and solve problems.
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Chapter 14 Formulae
Learning Objectives • Write expressions in algebra • Write a formula • Know the difference between expressions & formula • Substitute values into formulae and evaluate • Substitute values into formulae with powers & roots • Re-arrange formulae • Solve problems by re-arranging formulae
Writing Expressions & Formulae • An expression does not have an equal sign • A formula does have an equal sign Examples • A box of matches has 55 matches, write an expression for the total matches in n boxes. • Write a formula for the total perimeter, P, of a shape with sides x – 3, x+ 2 & x
Substituting in Formula Examples • 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)
Formulae with Powers & Roots Examples • Find the value of S = (½p)3, when (a) p = 4 (b) p = -4 • Calculate √(5x) when x = 0.4 • Use the formula v = √(u2 + 2as) to find the value of v when a = -9.8, s = 1.67 and u = 45.3
Re-arranging Formulae • Remember that when moving terms to the other side you do the opposite Examples • Make m the subject in k = 8m/5 • Make x the subject in y = 2x + 8 • Make r the subject in A = 3r2 • Make b the subject in T = a + √b
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 = ½mv2 (d) a(b + x) = b(2a – x)
Solving Problems by Re-arranging • The volume of a cuboid, with length 7.8cm and breadth 5cm, is 136.5cm3. Calculate the height of the cuboid. • V = 4/3πr3. Calculate r when the volume is 3.56×104.