Formulas pack a rule into a few symbols, but each one is written to answer a single question. This course teaches you to rearrange a formula so that it answers the question you actually have. It begins with the words formula, variable, constant and subject, and with putting numbers into a formula. You then change the subject using inverse operations in reverse order, clear fractions and brackets, undo squares and square roots, and handle formulas where the new subject appears twice by taking it out as a common factor. The last lesson combines rearranging and substituting, the do-as-directed questions found in exams.
Middle Years
Changing the Subject of a Formula
What a formula and its subject are, how to rearrange a formula with inverse operations, fractions, brackets, squares and roots, what to do when the subject appears twice, and how to answer do-as-directed questions.
- 6 lessons
Overview
Lessons
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Formulas and their subjects
What a formula is, variables and constants, the subject of a formula, putting numbers into a formula in the right order, and writing a formula from words.
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Changing the subject with inverse operations
Undo the operations around the new subject in reverse order, using a flow chart, and check the rearranged formula with numbers. Includes v = u + at and P = 2(l + b).
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Formulas with fractions and brackets
Clear fractions by multiplying by the denominator, free a bracket by dividing by its multiplier, and rearrange the interest, temperature and trapezium formulas.
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Formulas with squares and square roots
Undo a square with a square root and a root by squaring: radius from area, the cylinder, v² = u² + 2as, kinetic energy, Pythagoras and the pendulum.
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When the subject appears twice
Gather every term containing the new subject on one side, take it out as a common factor and divide. Includes the amount formula and the lens formula.
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Rearranging and substituting: do as directed
Substitute first or rearrange first, answer do-as-directed questions on speed, temperature, interest and volume, and check that the answer makes sense.