MCQ
Let $f(x)=(x-a)^2+(x-b)^2+(x-c)^2.$ Then, $f(x)$ has a minimum at $x=$
  • $\frac{\text{a}+\text{b}+\text{c}}{3}$
  • B
    $\sqrt[3]{\text{a}\text{b}\text{c}}$
  • C
    $\frac{3}{\frac{1}{\text{a}}+\frac{1}{\text{b}}+\frac{1}{\text{c}}}$
  • D
    None of these.

Answer

Correct option: A.
$\frac{\text{a}+\text{b}+\text{c}}{3}$
$f(x)=(x-a)^2+(x-b)^2+(x-c)^2$
$\Rightarrow 2(x-a)+2(x-b)+2(x-c)$
to find minima or maxima $f ^{\prime}(x)=0$
$2(x-a)+2(x-b)^2+2(x-c)=0$
$\Rightarrow x=\frac{a+b+c}{3}$
$f^{\prime \prime}(x)=6>0$
function has minima at $\text{x}=\frac{\text{a}+\text{b}+\text{c}}{3}$.

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