MYTUTOR SUBJECT ANSWERS

562 views

The first three terms of a sequence are a, b, c. The term-to-term rule of the sequence is 'Multiply by 2 and subtract 4'. Show that c = 4(a – 3).

As the answer is given in the question, it's really important that you lay out your working carefully to give a convincing account as to how you got from the question to the answer. 

Here we have a sequence. This means that there is a fixed rule that determines how you get from one number to the next... or here, from one letter to the next, because the question is using an algebraic progression.  

The first letter in our sequence is a. To get to b we must multiply by 2 and subtract 4. a multiplied by 2 is 2a, and then subtracting 4 gives 2a - 4. Therefore, b = 2a-4. 

To get to the third letter in our sequence, c, we must take b and again multiply by 2 and subtract 4. As b = 2a-4, we must multiply this by 2, giving 2(2a-4) and then subtract 4, giving 2(2a-4) - 4. It is very important here to consider the brackets. Remember that we are doubling b, and so we must double the entire expression that we now have for b, and so we put brackets around it. 

So now we have c = 2(2a-4) - 4. This isn't quite the expression that we are working towards, but we can get there by expanding and then re-factorising. To expand the bracket, we multiply everything inside it by 2. This gives 4a - 8. Subtracting the other 4 gives c = 4a - 12. We can now go straight to the answer in the question, because both terms of the expression (4a and -12) are divisible by 4, giving c = 4((4a/4) - (12/4)) = 4(a-3). 
 

Robin B. GCSE Maths tutor, GCSE Biology tutor, A Level Biology tutor,...

10 months ago

Answered by Robin, a GCSE Maths tutor with MyTutor


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

630 SUBJECT SPECIALISTS

£18 /hr

Tamara A.

Degree: Medicine (Bachelors) - Liverpool University

Subjects offered:Maths, Chemistry+ 1 more

Maths
Chemistry
Biology

“I'm a friendly second year medical student with a year's experience in tutoring. I'm passionate about science, and I'm patient and approachable.”

MyTutor guarantee

£18 /hr

Matthew A.

Degree: BA Biological Sciences (Bachelors) - Oxford, Magdalen College University

Subjects offered:Maths, Physics+ 3 more

Maths
Physics
German
Chemistry
Biology

“Chatty, patient and enthusiastic Oxford Biology student. I did my A Levels just last year (A*A*A*A), so I can share my revision experience to help you achieve!”

MyTutor guarantee

£18 /hr

Diana B.

Degree: Chemistry (Masters) - Imperial College London University

Subjects offered:Maths, Chemistry+ 1 more

Maths
Chemistry
-Personal Statements-

“Imperial College London student giving Chemistry, Mathematics and Biology lessons”

MyTutor guarantee

About the author

Robin B. GCSE Maths tutor, GCSE Biology tutor, A Level Biology tutor,...
£22 /hr

Robin B.

Degree: Medicine (Bachelors) - Oxford, Merton College University

Subjects offered:Maths, Science+ 6 more

Maths
Science
Physics
Chemistry
Biology
.BMAT (BioMedical Admissions)
-Oxbridge Preparation-
-Medical School Preparation-

“About me  Hello! My name is Robin and I'm a 3rd year Medical Student at Oxford University. I have loads of experience working with, supporting and motivating young people of different ages. This includes being a volunteer assistant co...”

You may also like...

Other GCSE Maths questions

When would I use the quadratic formula?

Solve the quadratic equation x^2 + 4x +1 = 0 by completing the square.

The normal price of a television is £1200. It is reduced to £970. Work out the percentage reduction. Give your answer to 1 decimal place.

What is the Pythagoras Theorem?

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