The polynomial $f(x)=ax^3+bx-c$ is divisible by the polynomial $g(x)=x^2+bx+c$. Find the value of $ab$.


Given: The polynomial $f(x)=ax^3+bx-c$  is divisible by the polynomial $g(x)=x^2+bx+c$. 

To do: To find the value of $ab$.

Solution:

As given, the polynomial $f(x)=ax^3+bx-c$  is divisible by the polynomial $g(x)=x^2+bx+c$. 

By long division:

We find Remainder$=( ab^2+b-ac)x+( abc-c)

$\because f( x)$ is divisible by $g( x)$, remainder should be $0$.

$\Rightarrow ( ab^2+b-ac)x+( abc-c)=0$

$\Rightarrow ( ab^2+b-ac)x=0$ and $( abc-c)=0$

If $( abc-c)=0$

$\Rightarrow abc=c$

$\Rightarrow ab=1$

Thus, $ab=1$

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Updated on: 10-Oct-2022

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