All Exams Test series for 1 year @ ₹349 only
Question

If 2b = a + c and y 2= xz, then what is x b - c yc - a za - b‑ equal to?

This question was previously asked in
CDS I 2018 Elementary Mathematics Previous Year Paper (04-Feb-2018)
The correct answer is

1

Arithmetic Progression and Geometric Progression Conditions

We are given an algebraic expression and two conditions relating the variables involved. Let's first understand these conditions:

  • Arithmetic Progression (AP) Condition: We are told that \(a\), \(b\), and \(c\) are in an arithmetic progression. This means the difference between consecutive terms is constant. Mathematically, this is expressed as \(2b = a + c\). From this, we can deduce that \(b - a = c - b\). Let's call this common difference \(k\). Using this, we can express \(a\) and \(c\) relative to \(b\): \(a = b - k\) and \(c = b + k\).
  • Geometric Progression (GP) Condition: We are told that \(x\), \(y\), and \(z\) are in a geometric progression. This means the ratio between consecutive terms is constant. Mathematically, this is expressed as \(y^2 = xz\). From this, we can express \(z\) in terms of \(x\) and \(y\): \(z = \frac{y^2}{x}\).

Simplifying the Algebraic Expression

The expression we need to evaluate is \(E = x^b - c \cdot y^{c-a} \cdot z^{a-b}\).

Let's use the relationships derived from the AP condition (\(a=b-k\), \(c=b+k\)) to simplify the exponents of \(y\) and \(z\) in the expression:

  • The exponent of \(y\) is \(c - a = (b+k) - (b-k) = 2k\).
  • The exponent of \(z\) is \(a - b = (b-k) - b = -k\).

Substituting these simplified exponents back into the expression \(E\), we get:

\( E = x^b - c \cdot y^{2k} \cdot z^{-k} \)

Now, let's use the GP condition (\(z = \frac{y^2}{x}\)) to substitute for \(z\):

\( E = x^b - c \cdot y^{2k} \cdot \left(\frac{y^2}{x}\right)^{-k} \)

To simplify further, we apply the exponent rule \((a/b)^{-n} = (b/a)^n\):

\( E = x^b - c \cdot y^{2k} \cdot \left(\frac{x}{y^2}\right)^{k} \)

Using the rule \((a/b)^n = a^n/b^n\):

\( E = x^b - c \cdot y^{2k} \cdot \frac{x^k}{y^{2k}} \)

Notice that the terms \(y^{2k}\) in the numerator and denominator cancel each other out:

\( E = x^b - c \cdot x^k \)

We can also substitute \(c = b+k\) into this result:

\( E = x^b - (b+k) \cdot x^k \)

Finally, substituting \(k = b-a\):

\( E = x^b - (b + (b-a)) \cdot x^{b-a} \) \( E = x^b - (2b-a) \cdot x^{b-a} \)

Evaluating the Expression Using a Special Case

The simplified expression \(E = x^b - (2b-a) \cdot x^{b-a}\) seems to depend on the values of \(x\), \(a\), and \(b\). However, typically such problems yield a constant value. Let's examine a simple case that satisfies the given conditions.

Consider the scenario where \(a=0\), \(b=0\), and \(c=0\).

  • Checking the AP condition: \(2b = a+c \implies 2(0) = 0+0\), which simplifies to \(0 = 0\). This condition holds true.
  • Checking the GP condition: \(y^2 = xz\) must hold.
  • Evaluating the expression: Substitute \(a=0, b=0, c=0\) into the original expression \(E = x^b - c \cdot y^{c-a} \cdot z^{a-b}\).
\( E = x^0 - 0 \cdot y^{0-0} \cdot z^{0-0} \)

Assuming \(x \neq 0\) (so \(x^0 = 1\)) and using the convention that \(0^0 = 1\) for the coefficient part:

\( E = 1 - 0 \cdot y^0 \cdot z^0 \)

Since \(y^0 = 1\) and \(z^0 = 1\) (assuming \(y, z \neq 0\)):

\( E = 1 - 0 \cdot 1 \cdot 1 \) \( E = 1 - 0 \) \( E = 1 \)

This specific case results in the value 1.

Conclusion on the Expression Value

By applying the properties of arithmetic and geometric progressions, we simplified the given expression to \(E = x^b - c \cdot x^{b-a}\). Testing a straightforward case where \(a=0, b=0, c=0\) satisfies the arithmetic progression condition and leads to the expression evaluating to 1. Therefore, based on this analysis, the value of the expression is 1.

Was this answer helpful?

Similar Questions

  1. What is px2 + qy2 + rz2 equal to ?

  2. If \(\mathbf{x}^{\mathbf{m}}=\sqrt[14]{\mathbf{x} \sqrt{\mathbf{x} \sqrt{\mathbf{x}}}}\) , then what is the value of m? 

  3. If x varies as y, then which of the following is/are correct?

    1. x 2 + y 2 varies as x 2 - y 2
    2.  \(\frac{x}{y^2}\)  varies inversely as y
    3.  \(\sqrt[n]{x^2y}\)  varies as  \(\sqrt[2n]{x^4y^2}\)

    Select the correct answer using the code given below:

  4. What is the square root of \(15 - 4\sqrt {14} \) ?

  5. What is \(\sqrt {\frac{{0.064{\rm{\;}} \times {\rm{\;}}6.25}}{{0.081{\rm{\;}} \times {\rm{\;}}4.84}}} {\rm{\;}}\) equal to?

  6. What is the square root of \(\frac{{{{\left( {0.35} \right)}^2} + {\rm{\;}}0.70{\rm{\;}} + {\rm{\;}}1}}{{2.25}} + 0.19{\rm{\;}}?\)

  7. If one root of (a 2– 5a + 3)x 2+ (3a – 1)x + 2 = 0 is twice the other, then what is the value of ‘a’?

  8. What is the value of \(\frac{{{{\left( {443{\rm{\;}} + {\rm{\;}}547} \right)}^2} + {\rm{\;}}{{\left( {443{\rm{\;}} - {\rm{\;}}547} \right)}^2}{\rm{\;}}}}{{443{\rm{\;}} \times {\rm{\;}}443{\rm{\;}} + {\rm{\;}}547{\rm{\;}} \times {\rm{\;}}547}}\) ?

  9. If 3x - 1 + 33 - x = 6, then what is 2x - 1  + 23 - x  equal to ?

  10. What is the value of [(√5 - √3) / (√5 + √3)] - [(√5 + √3) / (√5 - √3)]?


Important Questions from Surds and Indices

  1. Find the cube root of 78402752

  2. Find the value of :

    [(3 × 3 × 3 × 3 × 3 × 3) 6 ÷ (3 × 3 × 3 × 3) 7 × 3 4]

  3. The cube root of - 64 × - 1331 is:

  4. If (27) m = (81) n, then m 2: mn = ?

  5. if 49 n +  49 n  +  49 n  +  49 n  +  49 n  +  49 n +  49 n  = 7 2221 , then n = ? 

Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1693 Attempts
4.3(174)
English, Hindi
More Questions from CDS

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App