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2. Polynomials
medium
For what value of $m$ is $x^{3}-2 m x^{2}+16$ divisible by $x+2 ?$
Option A
Option B
Option C
Option D
Solution
If $x^{3}-2 m x^{2}+16$ is divisible by $x+2,$ then $x+2$ is a factor of $x^{3}-2 m x^{2}+16.$
Now, let $\quad p(x)=x^{3}-2 m x^{2}+16.$
As $x+2=x-(-2)$ is a factor of $x^{3}-2 m x^{2}+16.$
So $\quad p(-2)=0.$
Now, $\quad p(-2)=(-2)^{3}-2 m(-2)^{2}+16.$
$=-8-8 m+16=8-8 m$
Now, $\quad p(-2)=0$
$\Rightarrow \quad 8-8 m=0$
$\Rightarrow \quad m=8 \div 8$
$\Rightarrow \quad m=1$
Hence, for $m +1, x +2$ is a factor of $x^{3}-2 m x^{2}+16,$ so $x^{3}-2 m x^{2}+16$ is completely divisible by $x+2.$
Standard 9
Mathematics