MYTUTOR SUBJECT ANSWERS

589 views

How do you change the subject of the formula?

​All that changing the subject of the formula means is basically getting a letter on its own on one side of the equation. To begin, let's take a relatively simple example.

Make x the subject of the formula:

4y + 2 = x - 4 

What this question basically means is get x on its own. At the moment on the right hand side we have x - 4. So, because we want x on its own what we can do is add 4 to this side. However, we must then add 4 to the left hand side to balance the equation (remember what we do to one side when changing the subject of the formula WE MUST DO TO THE OTHER SIDE). This then gives us the following:

4y + 2 +4 = x

So our final answer is:

x = 4y + 6

We have successfully made x the subject of the formula. Now let's try something a little bit more challenging.

Make y the subject of the formula.

2y/5 - 3x = 2

First we must isolate the 2y/5. To do this we can add 3x to both sides to get rid of it on the left side and get 2y/5 on its own. This gives us:

2y/5 = 2 + 3x

Now, the 2y is divided by 5, therefore by doing the inverse function of division which is multiplication, we can get 2y on its own. So we can multiply both sides by 5.

2y/5 * 5 = 5 * (2 + 3x)

2y = 5(2 + 3x)

It's probably easier if these brackets are expand so:

2y = 10 + 15x

TIP: Remember to put brackets around 2 + 3x because both the 2 and the 3x are being multiplied by 5.

​Finally we must get y on its own. At the moment the y is being multiplied by 2. So we must do the inverse function and divide 2y by 2. Remember to divide by 2 on both sides.

2y / 2 = (10 + 15x) / 2

y = (10 + 15x) / 2

This can be simplified to:

y = 5 + 15x/2

This is because 10/2 = 5 and 15x2 =is just 15x/2.

We have now successfully made y the subject of the formula.

The key things to remember when changing the subject of the formula are:

 - All it means is get a letter on one side of the equation on its own

- Use inverses functions (+ and - are inverses of each other and so are * and /) to isolate the letter

​- Whatever you do to one side you must do to the other

Robbie T. GCSE Maths tutor, GCSE Geography tutor, GCSE Spanish tutor

10 months ago

Answered by Robbie, a GCSE Maths tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

539 SUBJECT SPECIALISTS

£22 /hr

Lucy B.

Degree: Anthropology (Doctorate) - Cambridge University

Subjects offered:Maths, Science+ 5 more

Maths
Science
Drama
Chemistry
Biology
-Personal Statements-
-Oxbridge Preparation-

“Enthusiastic Cambridge grad, with experience in Biology and Maths, passionate about helping students reach their potential and achieve the grades they deserve. ”

MyTutor guarantee

£24 /hr

Michelangelo M.

Degree: MMath Mathematics with Placement (Masters) - Bath University

Subjects offered:Maths, Italian+ 4 more

Maths
Italian
Further Mathematics
Computing
.STEP.
.MAT.

“Mathematics student at the University of Bath, willing to help you love this subject and improve your grades.”

£18 /hr

Seb C.

Degree: History and Politics (Bachelors) - York University

Subjects offered:Maths, History+ 1 more

Maths
History
English Literature

“Hi Everyone! I'm Seb and I am in first year studying History and Politics, both of which I am passionate about equally!”

MyTutor guarantee

About the author

Robbie T.

Currently unavailable: for regular students

Degree: BSc Geography with Study in Continental Europe (Bachelors) - Bristol University

Subjects offered:Maths, Spanish+ 1 more

Maths
Spanish
Geography

“About Me ​I am in my first year studying Geography at the University of Bristol. My degree gives me the opportunity to study in Europe for a year and I hope to go to Spain to improve my Spanish which I loved studying at A Level. In ...”

MyTutor guarantee

You may also like...

Posts by Robbie

How do you change the subject of the formula?

How do you conjugate regular AR, IR and ER verbs in the present tense?

What is globalisation and how does it affect us?

Other GCSE Maths questions

Solve 3x^2 = 8x - 2 giving your answers to 2 d.p.

How do you multiply an "number" with powers for example a^3 * a^6

How do you multiply out brackets

How do I know the best way to solve a quadratic equation?

View GCSE Maths tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok