# Math Help - Remainder Theorum

1. ## Remainder Theorum

hi all,

The remainder when $2x^3 + ax^2 + 4$ is dividied by $x - 2$ is five times more that when it is divided by $x - 1$.
Find a.

As far as i can see ( i remember to set x to a value that makes divisor 0 since dividend=divisor x quotient + remainder) :

$f(x)=2x^3+ax^2+4$

$f(1)=2+a+4$

$f(2)=16+4a+4$

and

$f(2)=5f(1)$

$20+4a = 5(6+a)$

$20+4a=30+5a$

$-10=a$

must be doing something stupid because the book says the answer is -3
thanks sammy

2. Everything is correct... Either your book's answer is wrong or you have copied the question incorrectly.

3. thanks for checking it Prove It.