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Question

The value of (x - y)(x + y) + (y - z)(y + z) + (z - x)(z + x) is:

This question was previously asked in
RRB NTPC 2024 Undergraduate CBT 1 Question Paper (29-Aug-2025) (Shift 1)
The correct answer is

0

Evaluating the Algebraic Expression (x - y)(x + y) + ...

The question asks for the value of the expression: \((x - y)(x + y) + (y - z)(y + z) + (z - x)(z + x)\) To solve this, we can use a fundamental algebraic identity known as the 'difference of squares'.

Applying the Difference of Squares Identity

The difference of squares identity states that for any two terms 'a' and 'b': \(a^2 - b^2 = (a - b)(a + b)\) We can apply this identity to each part of the given expression:

  • For the first term, let \(a=x\) and \(b=y\). Applying the identity, we get: \((x - y)(x + y) = x^2 - y^2\)
  • For the second term, let \(a=y\) and \(b=z\). Applying the identity, we get: \((y - z)(y + z) = y^2 - z^2\)
  • For the third term, let \(a=z\) and \(b=x\). Applying the identity, we get: \((z - x)(z + x) = z^2 - x^2\)

Simplifying the Expression

Now, we substitute these results back into the original expression:

\( (x^2 - y^2) + (y^2 - z^2) + (z^2 - x^2) \)

Let's rearrange the terms to group the like terms together:

\( x^2 - x^2 + y^2 - y^2 + z^2 - z^2 \)

Now, we can perform the subtraction for each pair of like terms:

  • \(x^2 - x^2 = 0\)
  • \(y^2 - y^2 = 0\)
  • \(z^2 - z^2 = 0\)

Adding these results together:

\( 0 + 0 + 0 = 0 \)

Therefore, the value of the expression \((x - y)(x + y) + (y - z)(y + z) + (z - x)(z + x)\) is 0.

Conclusion

By applying the difference of squares identity and simplifying the terms, we find that the entire expression evaluates to 0.

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Similar Questions

  1. For what value of K is the equation \(\frac{0.009}{K} = 0.1\) true?
  2. Arnab buys 9 oranges and 8 bananas for ₹276. When the cost of an orange is decreased by 10% and that of a banana remains the same, then the cost of 5 oranges and 10 bananas is ₹210. What is the original cost of 4 oranges and 3 bananas?
  3. If a + b = 7 and ab = 12, then \(a^2 + b^2\) is equal to:
  4. Reduce to linear form 

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Important Questions from Algebric Equations

  1. For what value of K is the equation \(\frac{0.009}{K} = 0.1\) true?
  2. Arnab buys 9 oranges and 8 bananas for ₹276. When the cost of an orange is decreased by 10% and that of a banana remains the same, then the cost of 5 oranges and 10 bananas is ₹210. What is the original cost of 4 oranges and 3 bananas?
  3. Find the value of x satisfying: $5(5x^2 - 5) - 5(5x^2 + 7x - 2) = 14$
  4. The product of two positive numbers is 3645. If the first number is five times the second number, then the sum of the two numbers is:
  5. The product of two positive numbers is 80. If the first number is five times of the second number, then the sum of the two numbers is:
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