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If one root of the equation |{:(7,6,x^(2...

If one root of the equation `|{:(7,6,x^(2)-13),(2,x^(2)-13,2),(x^(2)-13,3,7):}|` =0 is x=2 the sum of all other five roots is

A

`2sqrt(15)`

B

-2

C

`sqrt(20)+sqrt(15)-2`

D

None of these

Text Solution

AI Generated Solution

The correct Answer is:
To solve the given problem, we need to evaluate the determinant and find the roots of the resulting polynomial equation. Let's break this down step by step. ### Step 1: Set up the determinant We are given the determinant: \[ D = \begin{vmatrix} 7 & 6 & x^2 - 13 \\ 2 & x^2 - 13 & 2 \\ x^2 - 13 & 3 & 7 \end{vmatrix} \] ### Step 2: Calculate the determinant To calculate the determinant, we can use the formula for a 3x3 determinant: \[ D = a(ei - fh) - b(di - fg) + c(dh - eg) \] Where: - \( a = 7, b = 6, c = x^2 - 13 \) - \( d = 2, e = x^2 - 13, f = 2 \) - \( g = x^2 - 13, h = 3, i = 7 \) Calculating each part: 1. \( ei - fh = (x^2 - 13) \cdot 7 - 2 \cdot 3 = 7x^2 - 91 - 6 = 7x^2 - 97 \) 2. \( di - fg = 2 \cdot 7 - 2(x^2 - 13) = 14 - 2x^2 + 26 = 40 - 2x^2 \) 3. \( dh - eg = 2 \cdot 3 - (x^2 - 13)(x^2 - 13) = 6 - (x^2 - 13)^2 \) Now substituting back into the determinant formula: \[ D = 7(7x^2 - 97) - 6(40 - 2x^2) + (x^2 - 13)(6 - (x^2 - 13)^2) \] ### Step 3: Simplify the determinant Now we simplify \( D \): \[ D = 49x^2 - 679 - 240 + 12x^2 + (x^2 - 13)(6 - (x^4 - 26x^2 + 169)) \] We need to expand and combine like terms to obtain a polynomial in \( x \). ### Step 4: Set the determinant equal to zero Since we know that one root is \( x = 2 \), we can substitute \( x = 2 \) into the polynomial to verify it is a root and then find the sum of the other roots. ### Step 5: Use Vieta's formulas The polynomial will be of degree 6, and by Vieta's formulas, the sum of the roots of the polynomial \( ax^6 + bx^5 + ... = 0 \) is given by \( -\frac{b}{a} \). ### Step 6: Determine the sum of the other roots Since \( x = 2 \) is one of the roots, we can denote the sum of the other five roots as \( S \). Thus, we have: \[ 2 + S = -\frac{b}{a} \] From the previous calculations, if \( b = 0 \) (since there is no \( x^5 \) term), then: \[ 2 + S = 0 \implies S = -2 \] ### Final Answer The sum of all other five roots is: \[ \boxed{-2} \]
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