Lesson video

Hi, I'm Ms.Davies.

In this lesson, we're going to be changing the subject of a formula that involves squares or square roots.

The subject of a formula is the singular variable, on one side of the equal symbol.

Let's have a look at a few examples.

In this example, Y is the subject as it is on its own on one side of the equal symbol.

In this next example, P is the subject.

In the final example, S is the subject.

In this example, we're making M the subject of this formula.

The inverse of squaring something, is the square root.

To make M the subject, we're going to find the square root of both sides.

This means that M is equal to the square root of P.

In our next example, we have got the square root of M, is equal to P.

As we've just said, the inverse of square root is to square.

So let's square both sides of our formula.

This gives us M is equal to P squared.

In this next example, we need to make M the subject again.

Let's start by subtracting Y from both sides.

This gives us, M squared is equal to P subtract Y.

We can now square root both sides to get M on its own.

This gives M is equal to the square root of P subtract Y.

Notice that both P and negative Y, are in the square root.

This is really important.

In our final example, we've got three M squared is equal to P.

Three M squared means three watts of M squared.

The first thing we're going to do, to make M the subject, is divide both sides by three.

This gives us M squared is equal to P divided by three.

Our next step is to square root both sides.

This gives us M is equal to the square root of P divided by three.

Here is some questions, for you to try.

Pause the video to complete your task, and resume once you're finished.

Here are the answers.

Make sure that your squares and square roots are in the correct places, and you've used brackets, where they are needed.

Here is a question for you to try.

Pause the video to complete your task, and resume once you're finished.

Here are the answers.

You should have divided both sides by three first, then added five, and finally squared rooted both sides.

This gives the answer, t equals the square root of X over three, add five, where all those terms are in the square root.

Here is some questions for you to try.

Pause the video to complete your task, and resume once you're finished.

Here are the answers.

G didn't need to square negative five.

The correct answer is G equals J squared, add five.

That's all for this lesson.

Thanks for watching.