Let $f(x)$ be a polynomial of degree three satisfying $f(0)=-1$ and $f(1)=0$. Also, 0 is a stationary point of $f(x)$. If $f(x)$ does not have an extremum at $x=0$, then the value of the integral $\int \frac{f(x)}{x^3-1} d x$, is |
$\frac{x^2}{2}+C$ $x+C$ $\frac{x^3}{6}+C$ none of these |
$x+C$ |
Let $f(x)=a x^3+b x^2+c x+d$. Then, $f(0)=-1$ and $f(1)=0$ $\Rightarrow d=-1$ and $a+b+c+d=0$ $\Rightarrow d=-1$ and $a+b+c=1$ ... (i) It is given that x = 0 is a stationary point of f(x) but it is not a point of extremum. Therefore, $f'(0)=0, f''(0)=0$ and $f'''(0) \neq 0$ Now, $f(x)=a x^3+b x^2+c x+d$ $\Rightarrow f'(x)=3 a x^2+2 b x+c, f''(x)=6 a x+b$ and $f'''(x)=6 a$ ∴ $f'(0)=0, f''(0)=0$ and $f'''(0) \neq 0$ $\Rightarrow c=0, b=0$ and $a \neq 0$ ....(ii) From (i) and (ii), we get $a=1, b=c=0$ and $d=-1$ ∴ $f(x)=x^3-1$ Hence, $\int \frac{f(x)}{x^3-1} d x=\int 1 . d x=x+C$ |