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If the roots of 27x^(4) - 195x^(3) + 494...

If the roots of `27x^(4) - 195x^(3) + 494x^(2) - 520x + 192 = 0 ` are in G.P. then the roots are

A

`-1,1,3,5`

B

`1,1,-3,-5`

C

`8/9 ,4/3,2,3`

D

`-2,1/2 ,3,1`

Text Solution

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The correct Answer is:
To solve the problem, we need to find the roots of the polynomial \(27x^4 - 195x^3 + 494x^2 - 520x + 192 = 0\) under the condition that the roots are in geometric progression (G.P.). ### Step 1: Understanding the Roots in G.P. Let the roots be \(a, ar, ar^2, ar^3\) where \(a\) is the first term and \(r\) is the common ratio of the G.P. ### Step 2: Using Vieta's Formulas According to Vieta's formulas, for a polynomial of the form \(ax^4 + bx^3 + cx^2 + dx + e = 0\), the relationships between the coefficients and the roots are as follows: - The sum of the roots: \(a + ar + ar^2 + ar^3 = -\frac{b}{a}\) - The sum of the products of the roots taken two at a time: \(a \cdot ar + a \cdot ar^2 + a \cdot ar^3 + ar \cdot ar^2 + ar \cdot ar^3 + ar^2 \cdot ar^3 = \frac{c}{a}\) - The product of the roots: \(a \cdot ar \cdot ar^2 \cdot ar^3 = \frac{e}{a}\) ### Step 3: Calculate the Product of the Roots The product of the roots is given by: \[ a \cdot ar \cdot ar^2 \cdot ar^3 = a^4 r^6 \] According to Vieta's, this is equal to: \[ \frac{192}{27} = \frac{64}{9} \] Thus, we have: \[ a^4 r^6 = \frac{64}{9} \] ### Step 4: Calculate the Sum of the Roots The sum of the roots is: \[ a(1 + r + r^2 + r^3) = a \cdot \frac{r^4 - 1}{r - 1} = -\frac{-195}{27} = \frac{195}{27} = \frac{65}{9} \] ### Step 5: Calculate the Sum of the Products of the Roots The sum of the products of the roots taken two at a time is: \[ a^2(r + r^2 + r^3 + r^2 + r^3 + r^4) = a^2 \cdot \frac{r^6 - 1}{r - 1} = \frac{494}{27} \] ### Step 6: Solving for Roots Now we need to find values of \(a\) and \(r\) that satisfy these equations. From the product equation: \[ a^4 r^6 = \frac{64}{9} \] Assuming \(a = \frac{2}{3}\) and \(r = 2\), we can check: \[ \left(\frac{2}{3}\right)^4 \cdot 2^6 = \frac{16}{81} \cdot 64 = \frac{1024}{81} \neq \frac{64}{9} \] We can try different values for \(a\) and \(r\) until we find a combination that satisfies all equations. ### Step 7: Testing Options Given the options, we can test the combinations: 1. \(2, 3, \frac{4}{3}, \frac{8}{9}\) 2. \(1, 2, 3, 4\) 3. \(4, 2, \frac{8}{9}, \frac{4}{3}\) After testing, we find that: - The combination \(2, \frac{4}{3}, \frac{8}{9}, 3\) satisfies all conditions. ### Conclusion Thus, the roots of the equation \(27x^4 - 195x^3 + 494x^2 - 520x + 192 = 0\) that are in G.P. are: \[ \frac{8}{9}, \frac{4}{3}, 2, 3 \]
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