Question
If there is a statement involving the natural number n such that:
  1. The statement is true for n = 1
  2. When the statement is true for n = k (where k is some positive integer), then the statement is also true for n = k + 1.
Then, the statement is true for all natural numbers n.
Also, if A is a square matrix of order n, then A2 is defined as AA. In general, Am = AA .... A (m times). where m is any positive integer.
Based on the above information, answer the following questions.
  1. If $\text{A}=\begin{bmatrix}3&-4\\1&-1\end{bmatrix},$ then for any positive integer n,
  1. $\text{A}^\text{n}=\begin{bmatrix}3\text{n}&-4\text{n}\\\text{n}&-\text{n}\end{bmatrix}$
  2. $\text{A}^\text{n}=\begin{bmatrix}1+2\text{n}&-4\text{n}\\\text{n}&1-2\text{n}\end{bmatrix}$
  3. $\text{A}^\text{n}=\begin{bmatrix}3\text{n}&-8\text{n}\\1&-\text{n}\end{bmatrix}$
  4. $\text{A}^\text{n}=\begin{bmatrix}1+3\text{n}&-4\text{n}\\\text{n}&1-3\text{n}\end{bmatrix}$
  1. If $\text{A}=\begin{bmatrix}1&2\\0&1\end{bmatrix},$ then |An|, where $\text{n}\in\text{ N},$ is equal to:
  1. 2n
  2. 3n
  3. n
  4. 1
  1. If $\text{A}=\begin{bmatrix}1&0\\1&1\end{bmatrix}$ and $\text{I}=\begin{bmatrix}1&0\\0&1\end{bmatrix}$ then which of the following holds for all natural numbers $\text{n}\geq1?$
  1. A= nA - (n - 1)I
  2. An = 2n-1 A - (n - 1)I
  3. A= nA + (n - 1)I
  4. An = 2n-1 A + (n - 1)I
  1. Let $\text{A}=\begin{bmatrix}\text{a}&0&0\\0&\text{a}&0\\0&0&\text{a}\end{bmatrix}$ and $\text{A}^\text{n}=[\text{a}_{\text{ij}}]_{3\times3}$ for some positive integer n, then the cofactor of a13 is:
  1. an
  2. -an
  3. 2an
  4. 0
  1. If A is a square matrix such that |A| = 2, then for any positive integer n, |An| is equal to:
  1. 0
  2. 2n
  3. 2n
  4. n2

Answer

  1. (b) $\text{A}^\text{n}=\begin{bmatrix}1+2\text{n}&-4\text{n}\\\text{n}&1-2\text{n}\end{bmatrix}$

Solution:

We have, $\text{A}=\begin{bmatrix}3&-4\\1&-1\end{bmatrix}$

$\therefore\text{A}^2=\begin{bmatrix}3&-4\\1&-1\end{bmatrix}\begin{bmatrix}3&-4\\1&-1\end{bmatrix}=\begin{bmatrix}5&-8\\2&-3\end{bmatrix},$ which can be obtained from $\text{A}^\text{n}=\begin{bmatrix}1+2\text{n}&-4\text{n}\\\text{n}&1-2\text{n}\end{bmatrix}$ for n = 2.

  1. (d) 1

Solution:

We have, $\text{A}=\begin{bmatrix}1&2\\0&1\end{bmatrix}$

$\therefore|\text{A}|=\begin{vmatrix}1&2\\0&1\end{vmatrix}=1-0=1$

Also, |An| = |A· A ...... A(n times)| = |A|n = 1n = 1

  1. (a) A= nA - (n - 1)I

Solution:

For n = 1, all options are true.

$\text{A}^2=\text{A}\cdot\text{A}=\begin{bmatrix}1&0\\1&1\end{bmatrix}\begin{bmatrix}1&0\\1&1\end{bmatrix}=\begin{bmatrix}1&0\\2&1\end{bmatrix}$

and $\text{A}^3=\text{A}^2\cdot\text{A}=\begin{bmatrix}1&0\\2&1\end{bmatrix}\begin{bmatrix}1&0\\1&1\end{bmatrix}=\begin{bmatrix}1&0\\3&1\end{bmatrix}$

Putting n = 3, in (a), we get A3 = 3A - 2I

$=3\begin{bmatrix}1&0\\1&1\end{bmatrix}-\begin{bmatrix}2&0\\0&2\end{bmatrix}$

$=\begin{bmatrix}3&0\\3&3\end{bmatrix}-\begin{bmatrix}2&0\\0&2\end{bmatrix}=\begin{bmatrix}1&0\\3&1\end{bmatrix},$ which is true.

All other options are different from A3 = 3A -2I for n = 3.

  1. (d) 0

Solution:

We have, $\text{A}=\begin{bmatrix}\text{a}&0&0\\0&\text{a}&0\\0&0&\text{a}\end{bmatrix}$

$\therefore\text{A}^2=\text{A}\cdot\text{A}=\begin{bmatrix}\text{a}&0&0\\0&\text{a}&0\\0&0&\text{a}\end{bmatrix}\begin{bmatrix}\text{a}&0&0\\0&\text{a}&0\\0&0&\text{a}\end{bmatrix}$

$=\begin{bmatrix}\text{a}^2&0&0\\0&\text{a}^2&0\\0&0&\text{a}^2\end{bmatrix}$

Similarly, $\text{A}^\text{n}=\begin{bmatrix}\text{a}^\text{n}&0&0\\0&\text{a}^\text{n}&0\\0&0&\text{a}^\text{n}\end{bmatrix}$

Now, cofactor of $\text{a}_{13}=(-1)^{1+3}\begin{vmatrix}0&\text{a}^\text{n}\\0&0\end{vmatrix}=0$

  1. (c) 2n

Solution:

We have, |A| = 2 and |An| = |A·A ...... A(n - times)|

= |A| |A| ...... |A|(n - times) = |A|n = 2n

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  3. $\frac{\text{x}+3}{1}=\frac{\text{y}+2}{-2}=\frac{\text{z}-1}{2}$

  4. None of these
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Based on the above information, answer the following questions.

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  3. 20%
  4. 25%
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  1. $\frac{1}{2}$

  2. $\frac{1}{5}$

  3. $\frac{3}{5}$

  4. $\frac{1}{3}$

  1. Find the probability that puzzle is solved.
  1. $\frac{1}{2}$

  2. $\frac{1}{5}$

  3. $\frac{2}{5}$

  4. $\frac{5}{6}$

  1. Probability that exactly one of them solved the puzzle, is:
  1. $\frac{1}{30}$

  2. $\frac{1}{20}$

  3. $\frac{7}{20}$

  4. $\frac{3}{20}$

  1. Probability that none of them solved the puzzle, is:
  1. $\frac{1}{5}$

  2. $\frac{3}{5}$

  3. $\frac{2}{5}$

  4. None of these