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NDA 2016
Exam
NDA
Year
2016
Subject
Mathematics
Chapter
Determinants

NDA 2016 · Mathematics · Determinants

Which of the following determinants have value 'zero'? 1. | array...

Which of the following determinants have value 'zero'? 1. \left|411579792953\begin{array}{lll}41 & 1 & 5 \\ 79 & 7 & 9 \\ 29 & 5 & 3\end{array}\right| 2. \left|1ab+c1 bc+a1ca+b\begin{array}{lll}1 & \mathrm{a} & \mathrm{b}+\mathrm{c} \\ 1 & \mathrm{~b} & \mathrm{c}+\mathrm{a} \\ 1 & \mathrm{c} & \mathrm{a}+\mathrm{b}\end{array}\right| 3. \quad\left|0cb−c0a−b−a0\begin{array}{ccc}0 & \mathrm{c} & \mathrm{b} \\ -\mathrm{c} & 0 & \mathrm{a} \\ -\mathrm{b} & -\mathrm{a} & 0\end{array}\right| Select the correct answer using the code given below.

Options

  1. A1 and 2 only
  2. B2 and 3 only
  3. C1 and 3 only
  4. D1, 2 and 3

Correct answer

D. 1, 2 and 3

Step-by-step solution

1. ∣411579792953∣=∣401572792453∣C1→C1−C2=8∣515979353∣=0\begin{aligned} \left|\begin{array}{lll} 41 & 1 & 5 \\ 79 & 7 & 9 \\ 29 & 5 & 3 \end{array}\right| & =\left|\begin{array}{lll} 40 & 1 & 5 \\ 72 & 7 & 9 \\ 24 & 5 & 3 \end{array}\right| C_1 \rightarrow C_1-C_2 \\ & =8\left|\begin{array}{lll} 5 & 1 & 5 \\ 9 & 7 & 9 \\ 3 & 5 & 3 \end{array}\right|=0 \end{aligned}∵\because two columns are same so value of determinant is zero. 2. ∣1ab+c1bc+a1ca+b∣=∣1a+b+cb+c1a+b+cc+a1a+b+ca+b∣C2→C2+C3=(a+b+c)∣11b+c11c+a11a+b∣=0\begin{aligned} \left|\begin{array}{lll} 1 & a & b+c \\ 1 & b & c+a \\ 1 & c & a+b \end{array}\right| & =\left|\begin{array}{lll} 1 & a+b+c & b+c \\ 1 & a+b+c & c+a \\ 1 & a+b+c & a+b \end{array}\right| \quad C_2 \rightarrow C_2+C_3 \\ & =(a+b+c)\left|\begin{array}{lll} 1 & 1 & b+c \\ 1 & 1 & c+a \\ 1 & 1 & a+b \end{array}\right|=0 \end{aligned}∵\because two columns are same so value of determinant is zero. 3. \left|0cb−c0a−b−a0\begin{array}{ccc}0 & c & b \\ -c & 0 & a \\ -b & -a & 0\end{array}\right|=0\because diagonal is zero so value of determinant is zero.
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