Class 12

Let * be a binary operation on Q – {-1} defined by a * b = a + b + ab for all a, b ∈ Q – {-1}. Then, (i) Show that * is both commutative and associative on Q – {-1} (ii) Find the identity element in Q – {-1}

Answers: (i) Consider, a, b ∈ Q – {-1} a * b = a + b + ab = b + a + ba = b * a a * b = b * a, ∀ a, b ∈ Q – {-1}   a * (b * c) = a * (b + c + b c) = a + (b + c + b c) + a (b + c + b c) = a + b +...

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Let A = R0 × R, where R0 denote the set of all non-zero real numbers. A binary operation ‘O’ is defined on A as follows: (a, b) O (c, d) = (ac, bc + d) for all (a, b), (c, d) ∈ R0 × R. (i) Show that ‘O’ is commutative and associative on A (ii) Find the identity element in A

Answers: (i) Consider, X = (a, b) Y = (c, d) ∈ A, ∀ a, c ∈ R0 b, d ∈ R X O Y = (ac, bc + d) Y O X = (ca, da + b) X O Y = Y O X, ∀ X, Y ∈ A O is not commutative on A. X = (a, b) Y = (c, d) a Z = (e,...

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Let A = R0 × R, where R0 denote the set of all non-zero real numbers. A binary operation ‘O’ is defined on A as follows: (a, b) O (c, d) = (ac, bc + d) for all (a, b), (c, d) ∈ R0 × R. Find the invertible element in A.

Answer: Consider, F = (m, n) be the inverse in A ∀ m ∈ R0 and n ∈ R X O F = E F O X = E (am, bm + n) = (1, 0) and (ma, na + b) = (1, 0) Considering (am, bm + n) = (1, 0) am = 1 m = 1/a And bm + n =...

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Mark the tick against the correct answer in the following: The solution set of the equation $\left|\begin{array}{ccc}3 \mathrm{x}-8 & 3 & 3 \\ 3 & 3 \mathrm{x}-8 & 3 \\ 3 & 3 & 3 \mathrm{x}-8\end{array}\right|=0$ is
A. $\left\{\frac{2}{3}, \frac{8}{3}\right\}$
B. $\left\{\frac{2}{3}, \frac{11}{3}\right\}$
C. $\left\{\frac{3}{2}, \frac{8}{3}\right\}$
D. None of these

Solution: Option(B) To find: Value of $x$ We have, $\left|\begin{array}{ccc}3 x-8 & 3 & 3 \\ 3 & 3 x-8 & 3 \\ 3 & 3 & 3 x-8\end{array}\right|=0$ Applying $\mathrm{R}_{1}...

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Mark the tick against the correct answer in the following: The solution set of the equation $\left|\begin{array}{ccc}\mathrm{x}-2 & 2 \mathrm{x}-3 & 3 \mathrm{x}-4 \\ \mathrm{x}-4 & 2 \mathrm{x}-9 & 3 \mathrm{x}-16 \\ \mathrm{x}-8 & 2 \mathrm{x}-27 & 2 \mathrm{x}-64\end{array}\right|=0$ is
A. $\{4\}$
B. $\{2,4\}$
C. $\{2,8\}$
D. $\{4,8\}$

Solution: Option(A) To find: Value of $x$ We have, $\left|\begin{array}{ccc}x-2 & 2 x-3 & 3 x-4 \\ x-4 & 2 x-9 & 3 x-16 \\ x-8 & 2 x-27 & 3 x-64\end{array}\right|=0$ Applying...

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Mark the tick against the correct answer in the following: The solution set of the equation $\left|\begin{array}{ccc}\mathrm{x} & 3 & 7 \\ 2 & \mathrm{x} & 2 \\ 7 & 6 & \mathrm{x}\end{array}\right|=0$ is
A. $\{2,-3.7\}$
B. $\{2,7 .-9\}$
C. $[-2,3,-7\}$
D. none of these

Solution: Option(C) To find: Value of $x$ We have, $\left|\begin{array}{lll}\mathrm{x} & 3 & 7 \\ 2 & \mathrm{X} & 2 \\ 7 & 6 & \mathrm{x}\end{array}\right|=0$ Applying...

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Mark the tick against the correct answer in the following: $\left|\begin{array}{lll}\mathrm{a} & 1 & \mathrm{~b}+\mathrm{c} \\ \mathrm{b} & 1 & \mathrm{c}+\mathrm{a} \\ \mathrm{c} & 1 & \mathrm{a}+\mathrm{b}\end{array}\right|=?$
A. $a+b+c$
B. $2(a+b+c)$
C. $4 \mathrm{abc}$
D. $a^{2} b^{2} c^{2}$

Solution: Option(C) To find: Value of $\left|\begin{array}{lll}a & 1 & b+c \\ b & 1 & c+a \\ c & 1 & a+b\end{array}\right|$ We have, $\left|\begin{array}{lll}a & 1 &...

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Mark the tick against the correct answer in the following: $\left|\begin{array}{lll} \mathrm{bc} & \mathrm{b}+\mathrm{c} & 1 \\ \mathrm{ca} & \mathrm{c}+\mathrm{a} & 1 \\ \mathrm{ab} & \mathrm{a}+\mathrm{b} & 1 \end{array}\right|=?$
A. $(a-b)(b-c)(c-a)$
B. $-(a-b)(b-c)(c-a)$
C. $(a+b)(b+c)(c+a)$
D. None of these

Solution: Option(A) To find: Value of $\left|\begin{array}{lll}\mathrm{bc} & \mathrm{b}+\mathrm{c} & 1 \\ \mathrm{ca} & \mathrm{a}+\mathrm{c} & 1 \\ \mathrm{ab} &...

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Find the value of m for which the line $\overrightarrow r = (\widehat i + 2\widehat k) + \lambda (2\widehat i – m\widehat j – 3\widehat k)$ is parallel to the plane $\overrightarrow r .(m\widehat i + 3\widehat j + \widehat k) = 4$

Answer: Given equation of line, $\overrightarrow r  = (\widehat i + 2\widehat k) + \lambda (2\widehat i  - m\widehat j - 3\widehat k)$ Comparing with the line $\overrightarrow r  = \overrightarrow...

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Show that the line line $\overrightarrow r = (2\widehat i + 5\widehat j + 7\widehat k) + \lambda (\widehat i + 3\widehat j + 4\widehat k)$ is parallel to the plane $\overrightarrow r = (\widehat i + \widehat j – \widehat k) = 7$. Also, find the distance between them.

Answer: A line $\begin{array}{l} \overrightarrow r  = \overrightarrow a  + \lambda \overrightarrow b \\ \end{array}$ is parallel to the plane $\begin{array}{l} \overrightarrow r .\overrightarrow n ...

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Mark the tick against the correct answer in the following: $\left|\begin{array}{ccc} \sin \alpha & \cos \alpha & \sin (\alpha+\delta) \\ \sin \beta & \cos \beta & \sin (\beta+\delta) \\ \sin \gamma & \cos \gamma & \sin (\gamma+\delta) \end{array}\right|=?$
A. 0
B. 1
C. $\sin (\alpha+\delta)+\sin (\beta+\delta)+\sin (\gamma+\delta)$
D. none of these

Solution: Option(A) To find: Value of $\left|\begin{array}{lll}\operatorname{sind} & \cos \alpha & \sin (\alpha+\bar{\delta}) \\ \sin \beta & \cos \beta & \sin (\beta+\bar{\delta})...

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Mark the tick against the correct answer in the following: $\left|\begin{array}{cc} a+i b & c+i d \\ -c+i d & a-i d \end{array}\right|=?$
A. $\left(a^{2}+b^{2}-c^{2}-d^{2}\right)$
B. $\left(a^{2}-b^{2}+c^{2}-d^{2}\right)$
C. $\left(a^{2}+b^{2}+c^{2}+d^{2}\right)$
D. none of these

Solution: Option(C) To find: Value of $\left|\begin{array}{cc}a+i b & c+i d \\ -c+i d & a-i b\end{array}\right|$ Formula used: $\mathrm{i}^{2}=-1$ We have, $\left|\begin{array}{cc}a+i b...

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Mark the tick against the correct answer in the following: $\left|\begin{array}{cc} \sin 23^{\circ} & -\sin 7^{\circ} \\ \cos 23^{\circ} & \cos 7^{\circ} \end{array}\right|=?$
A. $\frac{\sqrt{3}}{2}$
B. $\frac{1}{2}$
C. $\sin 16^{\circ}$
D. $\cos 16^{\circ}$

Solution: Option(B) To find: Value of $\left|\begin{array}{cc}\sin 23^{\circ} & -\sin 7^{\circ} \\ \cos 23^{\circ} & \cos 7^{\circ}\end{array}\right|$ Formula used: (i) $\sin (A+B)=\sin A...

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