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

If \(\alpha\) and \(\beta\) are the roots of the equation \(\log_{10} [998+\sqrt{x^2-18x+76}] = 3\) then what is \((\alpha - \beta)^2\) equal to?

This question was previously asked in
CDS 2 2025 Maths Question Paper (14-Sep-2025)
The correct answer is
36

To solve the problem of finding \((\alpha - \beta)^2\) where \(\alpha\) and \(\beta\) are roots of the equation \(\log_{10} [998+\sqrt{x^2-18x+76}] = 3\), let's follow these steps:

  1. Start with solving the logarithmic equation: \(\log_{10} [998+\sqrt{x^2-18x+76}] = 3\).
  2. Convert the logarithmic form to exponential form: \(998+\sqrt{x^2-18x+76} = 10^3\).
  3. Calculate the power of 10: \(10^3 = 1000\).
  4. Substitute back to find the equation: \(998+\sqrt{x^2-18x+76} = 1000\) leads to \(\sqrt{x^2-18x+76} = 2\).
  5. Square both sides to eliminate the square root: \(x^2 - 18x + 76 = 4\).
  6. Reorganize the equation into a standard quadratic form: \(x^2 - 18x + 72 = 0\).
  7. For a quadratic equation of the form \(ax^2 + bx + c = 0\), the roots satisfy \(\alpha + \beta = -\frac{b}{a}\) and \(\alpha\beta = \frac{c}{a}\). Here, \(a = 1, b = -18, c = 72\).
  8. Calculate \(\alpha + \beta = 18\) and \(\alpha \beta = 72\).
  9. Use the identity for the square of the difference of roots: \((\alpha - \beta)^2 = (\alpha + \beta)^2 - 4\alpha\beta\).
  10. Substitute the known values:
    • \((\alpha + \beta)^2 = 18^2 = 324\)
    • \(4\alpha\beta = 4 \times 72 = 288\)
  11. Calculate: \((\alpha - \beta)^2 = 324 - 288 = 36\).

The value of \((\alpha - \beta)^2\) is therefore 36.

Was this answer helpful?

Similar Questions

  1. If \(a^b = b^a\), then what is 

    \(\frac{a \times   (\frac{a}{b}) ^{ \frac{a}{b} } }{ (a)^{ \frac{a}{b} } }\) 

    equal to?

  2. If \(x^4 + y^4 = 14x^2 y^2\), then consider the following : 

    I. \(\log_{10}(x^2 + y^2)\) = \(\log_{10} x + \log_{10} y + 2\log_{10} 2\) 

    II. \(\log_{10}(x^2-y^2)=\log_{10} x + \log_{10} y\) +\(\log_{10}2+0.5\log_{10} 3\) 

    Which of the above is/are correct?

  3. If \(\log_{10}2 = 0.301\) and \(\log_{10} 3 = 0.477\), then what is the number of digits in the expansion of \(60^{60}\) ?
  4. If log10(100001 - 4x)/(5 - x) = 1, then what is x equal to?

  5. What is √17 - 4√15 + √8 - 2√15 equal to?

  6. If \(\log_{10}(80)=p\), \(\log_{10}(45)=q\) and \(\log_{10}(216)=r\), then what is \(\log_{10}(384)\) equal to ?
  7. Consider the following statements in respect of common logarithms :

    I. The logarithm of a number greater than 100 but less than 1000 lies between 2 and 3.

    II. The logarithm of a positive number less than unity is negative.

    Which of the statements given above is/are correct?

  8. What is the number of zeros immediately after the decimal point in \((0.5)^{1000}\)? (Given that \(\log_{10}2 = 0.30103\))

  9. A sum of money at the rate of \(5\%\) per annum compounded annually becomes \(n\) times in \(100\) years. What is the value of \(n\)? (Given \(\log_{10}2=0.301\), \(\log_{10}3=0.477\) and \(\log_{10}7=0.845\))


Important Questions from Logarithms

  1. Given that $132^{0.14} = x$, $132^{0.26} = y$ and $x^z = y^2$, then the value of z is close to:

  2. For \(x \ge y > 1\), let \(\log_x\left(\frac{x}{y}\right) + \log_y\left(\frac{y}{x}\right) = k\), then the value of \(k\) can never be equal to

  3. If \(\log_ba = p\), \(\log_dc = 2p\) and \(\log_fe = 3p\), then what is \((ace)^{\frac{1}{p}}\) equal to ?

  4. What is the number of solutions of \(\log_4(x-1) = \log_2(x - 3)\)?
  5. Let \(p = \ln(x)\), \(q = \ln(x^3)\) and \(r = \ln(x^5)\), where \(x > 1\). Which of the following statements is/are correct?
    I. \(p, q\) and \(r\) are in AP.
    II. \(p, q\) and \(r\) can never be in GP.
    Select the answer using the code given below.
Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1767 Attempts
4.3(176)
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