Formulas and Equations (F)

You have to know how to SUBSTITUTE a value into a formula – you do this when you are told what value a variable has. Every time the letter appears in the formula, replace it with the number, remembering to keep the same relationships such as multiplying or adding.

The ‘subject’ of a formula is the variable that everything else is equal to. It is usually on the left-hand side of the equal sign, but it doesn’t have to be. You may be asked to ‘change the subject of the formula’ – this means you have to carry out algebraic manipulation to rearrange the variables. This is similar to solving equations, in that you are trying to remove everything from the variable that is to be the subject. However, they don’t just disappear, but have to appear on the other side of the equal sign, retaining the correct relationships with the other variables.