# Video: Pack 1 β’ Paper 3 β’ Question 1

Pack 1 β’ Paper 3 β’ Question 1

02:34

### Video Transcript

Make π the subject of the formula π equals two πΏ minus π over four.

Well, what Iβm gonna do is actually demonstrate a couple of methods to actually solving this problem. Okay, so weβve got π equals two πΏ minus π over four. So first of all, what Iβm gonna do is actually subtract two πΏ from each side. And when I actually do that, I get π minus two πΏ is equal to negative π over four.

The next stage is actually to multiply each side of the equation by four, because obviously we want π to be on its own. So when we do that, we get four multiplied by π minus two πΏ is equal to negative π.

So now if we actually look back at the question, we can see that we want π as the subject of the formula, not negative π. So therefore, what weβre gonna do is actually multiply each side of the equation by negative one. So therefore, weβre gonna get negative four multiplied by π minus two πΏ equals π.

So now if we actually expand the bracket, first of all weβre gonna get negative four multiplied by π, which gives us negative four π. And then we have negative four multiplied by negative two πΏ, which is gonna give us eight πΏ. Thatβs because a negative multiplied by a negative is a positive. So therefore, we get negative four π plus eight πΏ is equal to π. And then if we just swapped the equation around just so we can have π on the left-hand side, we see that π is equal to negative four π plus eight πΏ. So weβve made π the subject of the formula.

Okay, great! I said we shall use a couple of methods. So Iβm just using another method just to check. So again, weβre gonna start with π is equal to two πΏ minus π over four. So then the first stage is gonna be to add π over four, which will give us π plus π over four equals two πΏ. And the reason weβre doing this with this method is what weβre trying to do is actually avoid having a negative π, cause sometimes some students make mistakes when it comes to having a negative π.

Then next, what weβre gonna do is subtract π from each side. So therefore, weβre gonna have π over four is equal to two πΏ minus π. Then we multiply each side of the equation by four. And we get π is equal to four multiplied by two πΏ minus π. And then if we expand the bracket, we get π is equal to eight πΏ, because we got four multiplied by two πΏ, minus four π, and thatβs because we have four multiplied by negative π. So therefore, we get that π is equal to eight πΏ minus four π.

Letβs just rearrange this to have it in the same form as we had the first way working it out. So therefore, again, we get π is equal to negative four π plus eight πΏ. So therefore, weβve made π the subject of the formula and shown you two methods to do so.