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Question

If $x + y + z = 0$, then what will be the value of $\frac{x^2}{yz} + \frac{y^2}{zx} + \frac{z^2}{xy}$ ?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
3

The problem asks for the value of the expression $\frac{x^2}{yz} + \frac{y^2}{zx} + \frac{z^2}{xy}$ given the condition $x + y + z = 0$. We need to simplify the expression using the given condition.

Simplifying the Algebraic Expression

First, combine the terms in the expression by finding a common denominator, which is $xyz$.

  • Multiply the first term by $\frac{x}{x}$: $\frac{x^2}{yz} \times \frac{x}{x} = \frac{x^3}{xyz}$
  • Multiply the second term by $\frac{y}{y}$: $\frac{y^2}{zx} \times \frac{y}{y} = \frac{y^3}{xyz}$
  • Multiply the third term by $\frac{z}{z}$: $\frac{z^2}{xy} \times \frac{z}{z} = \frac{z^3}{xyz}$

Now, add the fractions:

$ \frac{x^3}{xyz} + \frac{y^3}{xyz} + \frac{z^3}{xyz} = \frac{x^3 + y^3 + z^3}{xyz} $

Using the Condition $x + y + z = 0$

We use the algebraic identity that states: If $a + b + c = 0$, then $a^3 + b^3 + c^3 = 3abc$.

In this problem, we are given $x + y + z = 0$. Applying the identity, we get:

$ x^3 + y^3 + z^3 = 3xyz $

Calculating the Final Value

Substitute the result from the identity ($x^3 + y^3 + z^3 = 3xyz$) back into the simplified expression:

$ \frac{x^3 + y^3 + z^3}{xyz} = \frac{3xyz}{xyz} $

Assuming $x, y,$ and $z$ are non-zero (to avoid division by zero in the original expression), we can cancel out $xyz$:

$ \frac{3xyz}{xyz} = 3 $

Therefore, the value of the expression is 3.

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