Algebraic Expressions · JHS3 Mathematics

Lesson notes

Learning Objectives

Indicator: B9.2.2.1.1 - Perform change of subject of a given formula and use it to solve problems.

By the end of the lesson, learners can:

Identify the subject of a given formula and state which variable needs to be isolated.
Apply inverse operations to rearrange a formula and make a specified variable the subject.
Rearrange formulae involving addition, subtraction, multiplication, division, squares and square roots.
Use a rearranged formula to solve practical problems involving area, volume and other real-life measurements.
Verify solutions by substituting the found value back into the original formula.

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Curriculum details

Strand: Algebra (Strand 2)
Sub-strand: Algebraic Expressions (2.2)
Content standard: B9.2.2.1 - Demonstrate an understanding of (i) change of subject (ii) substituting values to evaluate expressions, and (iii) factorize expressions that have simple binomial as a factor.
Indicator: B9.2.2.1.1 - Perform change of subject of a given formula and use it to solve problems.
Suggested placement: Term 2, Week 5 (Week 17 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: Mathematics, Common Core Programme (JHS1-JHS3), 2023, p. 183
Transcribed from the official NaCCA publication. Check this page against the source.

Exemplars (from the NaCCA curriculum)

E.g.1 Perform change of subject for given formulae
(i) Make x the subject of the following formulae

Wide black-and-white mathematical teaching visual is organised as a worked calculation with open white space around... — A wide black-and-white mathematical teaching visual is organised as a worked calculation with open white space around the main marks. Visible labels, values, and notation include: 1) q=x+7; 2) r=x-3; 3); 5x =s; 4); 3x+1; 2; =h; 32=*+1.

E.g.2 Use the concept of change of subject to solve problems involving formulae
i. The area of a rectangle is 24cm 2 . If the length is 8cm, find the value of the width.
ii. The formula for calculating the area of a circle is given as πr 2 . If a circle has an area of 154cm 2 , what is its radius?[take π = 22 ] 7
iii. The triangle below has an area of 54cm 2 . Find the value of the height of the triangle.
iv. The cylinder below has a volume of 330cm 3 . Find the value of the height

Triangle with base 18 and perpendicular height h stands beside a cylinder of diameter 10 cm and height h for a... — A triangle with base 18 and perpendicular height h stands beside a cylinder of diameter 10 cm and height h for a change-of-subject exercise. The wide colour table is arranged with horizontal divisions, vertical divisions, coloured regions.

of the cylinder. [take π = 22 ] 7