Matrices & Determinants
Matrices with entries from roots of quadratic — matrix match
MJAT_TS7_P1
Grade 12
Question:
Let $T=\{\alpha_1,\alpha_2,\beta\}$ be the 3 distinct roots of $x^2+x-1=0$ (note: a quadratic has at most 2 roots; here the set $T$ includes specific values). For a $3\times 3$ matrix $M=(a_{ij})$, let $R_i=a_{i1}+a_{i2}+a_{i3}$ and $C_j=a_{1j}+a_{2j}+a_{3j}$. Match entries in List-I with List-II:
P) Number of $M$ with all entries in $T$ such that $R_i=C_j=0$ for all $i,j$
Q) Number of symmetric $M$ with all entries in $T$ such that $C_j=0$ for all $j$
R) Skew-symmetric $M$ with $a_{ij}\in T$ for $i>j$ — number of solutions to $M(x,y,z)^T=(-a,a,0)^T$
S) $M$ with all entries in $T$, $R_i=0$ for all $i$ — absolute value of $\det(M)$
List-II: 1)1, 2)12, 3)∞, 4)6, 5)0
A) P→4, Q→2, R→5, S→1
B) P→2, Q→4, R→1, S→5
C) P→2, Q→4, R→3, S→5
D) P→1, Q→5, R→3, S→4
Step-by-Step Solution
Key Concept: P: Count $3\times 3$ matrices with entries from $T$ and all row/column sums = 0. Q: Symmetric with column sums 0. R: Skew-symmetric → $\det M=0$ → infinite or no solutions. S: Row sums 0 → $\det M=0\Rightarrow|\det M|=0$.
P→(2), Q→(4), R→(3), S→(5). Answer: **C**.
Correct Answer: C