˿

Equations and formulae – WJECSolving linear equations

Solve, form and manipulate algebraic expressions including simplifying and rearranging equations. Solve using trial and improvement.

Part of MathsAlgebra

Solving linear equations

Often in algebra we have an equation that we want to solve. This frequently involves manipulating the equation in various different ways to achieve a desired outcome.

The idea is frequently referred to as "change the side, change the sign" or similar, however these are just simplifications of the rule.

A good example of this is the simple equation 3\({y}\) = 12. If we want to find out the value of \({y}\), we must divide both sides of the equation by 3. We know that this is the operation when we have three lots of \({y}\) on one side of the equation, and we want to find the value of one lot of \({y}\).

Dividing both sides gives \({y}\) = 4. This is the solution to the equation.

Similarly if we have 5\({z}\) = 30, we divide both sides of the equation by 5 to give \({z}\) = 6.

If we had 8\({d}\) = 20, we would divide both sides of the equation by 8 to give \({d}\) = 2.5.

If we had 9\({s}\) = 108 we would divide both sides by 9 to give \({s}\) = 12.

We can also use this method to solve equations like \(\frac{j}{4}=~12\). This time we only have one quarter of \({j}\), as we want to just have "\({j}=\)" we must multiply both sides of the equation by 4. This would allow us to obtain the result \({j}~=~48\)

If we had \(\frac{k}{3}={7}\) we multiply both sides by 3 to obtain \({k}\) = 21.

If we had \(\frac{z}{8}={3.5}\) we multiply both sides by 8 to obtain \({z}\) = 28.

If we had \(\frac{b}{2.5}={10}\) we multiply both sides by 2.5 to obtain \({b}\) = 25.

What if we had, for example, \({-z}~=~{2}\)? We first have to realise the "\({-z}\)" is actually (–1) × \({z}\), so we would need to divide both sides of the equation by –1 leaving \({z}\) = –2.

Similarly if we had –3\({P}\) = –6 we would divide both sides of the equation by –3 leaving \({P}\) = 2.

If we had \(\frac{–R}{6}={3.2}\) we would need to multiply by –6 giving \({R}\) = –19.2.