MYTUTOR SUBJECT ANSWERS

54 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,...

1 month ago

Answered by Robin, a GCSE Maths tutor with MyTutor

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

328 SUBJECT SPECIALISTS

£18 /hr

Lorna P.

Degree: Veterinary Science (Bachelors) - Bristol University

Subjects offered: Maths, Chemistry+ 1 more

Maths
Chemistry
Biology

“Hello!  A bit about me.. I'm currently studying Veterinary Science at the University of Bristol, having previously completed a degree in Zoology at the University of Leeds. I'm a patient person and think teaching others is a very rew...”

MyTutor guarantee

£20 /hr

Amruni C.

Degree: Medicine (Bachelors) - Imperial College London University

Subjects offered: Maths, Science+ 1 more

Maths
Science
-Medical School Preparation-

“Hi, I’m Amruni and I’m a medical student at Imperial College London. For the past 2 years I have been tutoring Maths and Science to students from 11+ to GCSE and have absolutely loved being able to share my passion for science and mat...”

£22 /hr

Elicia T.

Degree: Security and Justice (Masters) - Leeds University

Subjects offered: Maths, Sociology+ 3 more

Maths
Sociology
Law
History
English

“My name is Elicia and I am currently studying a Law Masters in Security and Justice at the University of Leeds. I recently graduated from the same university with aLLB Law degree. My ambition is to complete a PhD in law and become a u...”

MyTutor guarantee

About the author

Robin B.

Currently unavailable: for new students

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

What is the largest possible length of a pole you could fit in a room?

Solve the inequality 6y+5>8?

Given 6x+2y=4 and 5x+y=8, solve the simultaneous equations to find x and y.

How do I draw a straight line graph given a y=mx+c equation by the table method?

View GCSE Maths tutors

Cookies:

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

mtw:mercury1:status:ok