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Substitute into common formulae

Lesson

Mathematicians love to write formulae as algebraic shorthand for expressions that we would otherwise have to write as a sentence.

For example, instead of writing, "The area of a rectangle is calculated by multiplying the length by the breadth," I can write the algebraic formula $$A=lb. Much shorter right! Formulae also makes it easier to substitute values and evaluate equations.

There are lots of topics that have common formulae: simple interest, area, volume, perimeter and temperature conversions just to name a few. Make sure your familiar with the formulae for your topic before you start doing exercises.

Here are some examples to get you started.

Examples

question 1

The perimeter of a square with side lengths of $$a is given by the formula $$P=4×a.

Find $$P if the length of each side is $$5 cm.

question 2

The area of a triangle is given by the formula $$A=12$$(base$$×height$$).

If the base of a triangle is $$3 cm and its height is $$10 cm, find its area.

Question 3

The simple interest generated by an investment is given by the formula $$I=P×R×T100.

Given that $$P=1000, $$R=6 and $$T=7, find the interest generated.

 

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