Sunday 1 December 2019

Does Polynomial Remainder Theorem work with divisors that are quadratic?



The Polynomial Remainder Theorem states that the remainder of the division of a polynomial $f(x)$ by a linear polynomial $x - r$ is equal to $f(r)$. In particular, $x-r$ divides $f(x) \iff f(r)=0$



But what if the divisor is not linear and of a degree higher than one?



Consider this question:





Let $\mathcal{P}(x)$ be any polynomial. When it is divided by $(x-13)$ and $(x-17)$, then the remainders are $15$ and $35$ respectively. The remainder, when $\mathcal{P}(x)$ is divided by $(x-13)(x-17)$, is




How I approached it:



$$\mathcal{P}(13)=15\tag1$$
$$\mathcal{P}(17)=35\tag2$$




But how do I figure out the remainder if the degree of the divisor is greater than one?


Answer



Alternative hint:
$$
\mathcal{P}(x)= g(x)(x-13)(x-17) + ax + b
$$

for some $\ a\ $ and $\ b\ $. Your recovered values of $\ \mathcal{P}(13)=15\ $ and $\ \mathcal{P}(17)=35\ $ give you two linear equations to solve for $ a\ $ and $\ b\ $.


No comments:

Post a Comment

real analysis - How to find $lim_{hrightarrow 0}frac{sin(ha)}{h}$

How to find $\lim_{h\rightarrow 0}\frac{\sin(ha)}{h}$ without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...