Slideshow 10, Mathematics Room 307, Mr Richard Sasaki Changing the Subject of Formulae

Objectives Review solving equations Understanding the benefit of changing the subject Know the meanings of “subject” and “in terms of” Being able to change the subject for given formulae with multiple unknowns

Solving Simple Equations Try the 5 minute worksheet for a warm up and review solving simple equations.

Answers

Changing the subject Here is a famous formula to calculate speed. If Koz Kondo takes 3 hours to run 27 kilometres, how fast did he run (as an average speed)? Okay, but how about if we want to calculate distance or time? We need to change the subject.

Changing the subject To change the subject, we need to keep everything balanced. One step is fine to change to distance or time. What do we do? To change for distance, we can see time is in the way. It’s dividing distance so we need to multiply it. x time So now we have a formula, distance = speed x time. We changed time because time was in the way.

Changing the subject Let’s change the subject to time from this equation as we can save a step. What do we do? Divide by speed! So by changing the subject, we were able to create three formulae, for speed, distance and time! Let’s try in some algebraic examples.

Changing the subject Here’s another example. First some vocabulary. And done! Let’s try another.

Let’s try this one. Changing the subject The order is exactly like equations, in this case, first take away 7 and then divide by 3 We write this as a fraction. And we swap!

Equations can contain more than 2 unknowns. Changing the subject Square root… And swap! Try the worksheets!

Answers q = 2p y and z