Math Is Fun Forum

danthemaths

Member

Registered: 2012-10-18

Posts: 2

The Remainder Theorem

hey guys, I am stuck on this question:
"The Remainder when x^3-2x^2+ax+5 is divided by x-3 is twice the remainder when the same expression is divided by x+1. Find the value of the constant a."
I know the answer is 4 but i dont know how to get there.

I have started it off but dont know what to from then on...

I worked out f(3) to be -14=3a
...and f(-1) to be a=2

Am I on the right lines? and what do I do from then on? this will really help me out

thanks in advance

danthemaths

Bob

Administrator

Registered: 2010-06-20

Posts: 10,648

Re: The Remainder Theorem

hi danthemaths

Welcome to the forum.

Am I on the right lines?

Not quite.

When you put x = 3 you get a remainder.  Let's say

and when x =-1

You are also told that

So make an equation from this and solve for a.

Hope that helps. 

?? But I'm not getting a = 4  ??

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob