Question : If $a+b+c=m$ and $\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=0$, then the average of $a^{2}, b^{2},$ and $c^{2}$ is:
Option 1: $m^{2}$
Option 2: $\frac{m^{2}}{3}$
Option 3: $\frac{m^{2}}{9}$
Option 4: $\frac{m^{2}}{27}$
Correct Answer: $\frac{m^{2}}{3}$
Solution : Given: $a+b+c=m$ Squaring both sides, we get, ⇒ $(a+b+c)^{2}=m^{2}$ ⇒ $a^{2}+b^{2}+c^{2}+2(ab+bc+ca)=m^{2}$ ------(1) [Using $(a+b+c)^{2} = a^{2}+b^{2}+c^{2}+2(ab+bc+ca)$ ] $\because\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=0$ ⇒ $\frac{bc+ac+ab}{abc}=0$ ⇒ $bc+ac+ab=0$ Putting the value of $bc+ac+ab=0$ in equation (1), we have, ⇒ $a^{2}+b^{2}+c^{2}+2(0)=m^{2}$ ⇒ $a^{2}+b^{2}+c^{2}=m^{2}$ Dividing by 3, both sides to find the average, ⇒ $\frac{a^{2}+b^{2}+c^{2}}{3}=\frac{m^{2}}{3}$ Hence, the correct answer is $\frac{m^{2}}{3}$.
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