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If a2abacbab2bcacbcc2=kalbmcn\begin{vmatrix} -a^2 & ab & ac \\ ba & -b^2 & bc \\ ac & bc & -c^2 \end{vmatrix} = k \cdot a^l b^m c^n, then

Match List-I with List-II

List-IList-II
(A) l=m=n=l = m = n =(I) 10
(B) k+l+m+n=k + l + m + n =(II) 6
(C) k2+l2+(mn)2=k^2 + l^2 + (m - n)^2 =(III) 2
(D) l2+m2+(nk)=l^2 + m^2 + (n - k) =(IV) 20

Choose the correct answer from the options given below:

Solution

Correct Option: 4

The determinant is:

a2abacbab2bcacbcc2\begin{vmatrix} -a^2 & ab & ac \\ ba & -b^2 & bc \\ ac & bc & -c^2 \end{vmatrix}

Factor out aa from Row 1, bb from Row 2, and cc from Row 3:

=abcabcabcabc= abc \begin{vmatrix} -a & b & c \\ a & -b & c \\ a & b & -c \end{vmatrix}


Expanding along Row 1:

abcabcabc=abcbcbacac+cabab\begin{vmatrix} -a & b & c \\ a & -b & c \\ a & b & -c \end{vmatrix} = -a \begin{vmatrix} -b & c \\ b & -c \end{vmatrix} - b \begin{vmatrix} a & c \\ a & -c \end{vmatrix} + c \begin{vmatrix} a & -b \\ a & b \end{vmatrix}

Calculate each 2×22 \times 2 determinant:

bcbc=(b)(c)(c)(b)=bcbc=0\begin{vmatrix} -b & c \\ b & -c \end{vmatrix} = (-b)(-c) - (c)(b) = bc - bc = 0

acac=a(c)(c)(a)=acac=2ac\begin{vmatrix} a & c \\ a & -c \end{vmatrix} = a(-c) - (c)(a) = -ac - ac = -2ac

abab=a(b)(b)(a)=ab+ab=2ab\begin{vmatrix} a & -b \\ a & b \end{vmatrix} = a(b) - (-b)(a) = ab + ab = 2ab


Substituting back:

=a(0)b(2ac)+c(2ab)= -a(0) - b(-2ac) + c(2ab)

=0+2abc+2abc= 0 + 2abc + 2abc

=4abc= 4abc


The complete determinant value:

Determinant=abc×4abc\text{Determinant} = abc \times 4abc

=4a2b2c2= 4a^2b^2c^2

Therefore: k=4k = 4, l=2l = 2, m=2m = 2, n=2n = 2


(A) l=m=n=2l = m = n = 2 matches with (III)

(B) k+l+m+n=4+2+2+2=10k + l + m + n = 4 + 2 + 2 + 2 = 10 matches with (I)

(C) k2+l2+(mn)2=42+22+(22)2=16+4+0=20k^2 + l^2 + (m - n)^2 = 4^2 + 2^2 + (2-2)^2 = 16 + 4 + 0 = 20 matches with (IV)

(D) l2+m2+(nk)=22+22+(24)=4+4+(2)=6l^2 + m^2 + (n - k) = 2^2 + 2^2 + (2-4) = 4 + 4 + (-2) = 6 matches with (II)


The correct matching is: (A) - (III), (B) - (I), (C) - (IV), (D) - (II)

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