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The sine of angle formed by the lateral ...

The sine of angle formed by the lateral face ADC and plane of the base ABC of the terahedron ABCD, where `A=(3,-2,1), B=(3, 1,5), C=(4,0,3) and D=(1,0,0)`, is :

A

`(2)/(sqrt(29))`

B

`(5)/(sqrt(29))`

C

`(3sqrt(3))/(sqrt(29))`

D

`(-2)/(sqrt(29))`

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The correct Answer is:
To find the sine of the angle formed by the lateral face ADC and the base ABC of the tetrahedron ABCD, we will follow these steps: ### Step 1: Identify the Points Given points are: - \( A = (3, -2, 1) \) - \( B = (3, 1, 5) \) - \( C = (4, 0, 3) \) - \( D = (1, 0, 0) \) ### Step 2: Calculate Vectors We need to calculate the vectors \( \overrightarrow{AD} \) and \( \overrightarrow{AC} \) for the lateral face ADC, and \( \overrightarrow{AB} \) and \( \overrightarrow{AC} \) for the base ABC. 1. **Calculate \( \overrightarrow{AD} \)**: \[ \overrightarrow{AD} = D - A = (1 - 3, 0 + 2, 0 - 1) = (-2, 2, -1) \] 2. **Calculate \( \overrightarrow{AC} \)**: \[ \overrightarrow{AC} = C - A = (4 - 3, 0 + 2, 3 - 1) = (1, 2, 2) \] 3. **Calculate \( \overrightarrow{AB} \)**: \[ \overrightarrow{AB} = B - A = (3 - 3, 1 + 2, 5 - 1) = (0, 3, 4) \] ### Step 3: Find Normal Vectors Next, we will find the normal vectors \( \mathbf{N_1} \) and \( \mathbf{N_2} \). 1. **Normal vector \( \mathbf{N_1} \) for face ADC**: \[ \mathbf{N_1} = \overrightarrow{AD} \times \overrightarrow{AC} \] \[ \mathbf{N_1} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ -2 & 2 & -1 \\ 1 & 2 & 2 \end{vmatrix} \] \[ = \mathbf{i}(2 \cdot 2 - (-1) \cdot 2) - \mathbf{j}(-2 \cdot 2 - (-1) \cdot 1) + \mathbf{k}(-2 \cdot 2 - 2 \cdot 1) \] \[ = \mathbf{i}(4 + 2) - \mathbf{j}(-4 + 1) + \mathbf{k}(-4 - 2) \] \[ = 6\mathbf{i} + 3\mathbf{j} - 6\mathbf{k} \] \[ \mathbf{N_1} = (6, 3, -6) \] 2. **Normal vector \( \mathbf{N_2} \) for base ABC**: \[ \mathbf{N_2} = \overrightarrow{AB} \times \overrightarrow{AC} \] \[ \mathbf{N_2} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 0 & 3 & 4 \\ 1 & 2 & 2 \end{vmatrix} \] \[ = \mathbf{i}(3 \cdot 2 - 4 \cdot 2) - \mathbf{j}(0 \cdot 2 - 4 \cdot 1) + \mathbf{k}(0 \cdot 2 - 3 \cdot 1) \] \[ = \mathbf{i}(6 - 8) - \mathbf{j}(0 - 4) + \mathbf{k}(0 - 3) \] \[ = -2\mathbf{i} + 4\mathbf{j} - 3\mathbf{k} \] \[ \mathbf{N_2} = (-2, 4, -3) \] ### Step 4: Calculate Cross Product Now we calculate \( \mathbf{N_1} \times \mathbf{N_2} \): \[ \mathbf{N_1} \times \mathbf{N_2} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 6 & 3 & -6 \\ -2 & 4 & -3 \end{vmatrix} \] \[ = \mathbf{i}(3 \cdot (-3) - (-6) \cdot 4) - \mathbf{j}(6 \cdot (-3) - (-6) \cdot (-2)) + \mathbf{k}(6 \cdot 4 - 3 \cdot (-2)) \] \[ = \mathbf{i}(-9 + 24) - \mathbf{j}(-18 - 12) + \mathbf{k}(24 + 6) \] \[ = 15\mathbf{i} + 30\mathbf{j} + 30\mathbf{k} \] ### Step 5: Calculate Magnitudes 1. **Magnitude of \( \mathbf{N_1} \)**: \[ |\mathbf{N_1}| = \sqrt{6^2 + 3^2 + (-6)^2} = \sqrt{36 + 9 + 36} = \sqrt{81} = 9 \] 2. **Magnitude of \( \mathbf{N_2} \)**: \[ |\mathbf{N_2}| = \sqrt{(-2)^2 + 4^2 + (-3)^2} = \sqrt{4 + 16 + 9} = \sqrt{29} \] 3. **Magnitude of \( \mathbf{N_1} \times \mathbf{N_2} \)**: \[ |\mathbf{N_1} \times \mathbf{N_2}| = \sqrt{15^2 + 30^2 + 30^2} = \sqrt{225 + 900 + 900} = \sqrt{2025} = 45 \] ### Step 6: Calculate Sine of the Angle Using the formula: \[ \sin(\theta) = \frac{|\mathbf{N_1} \times \mathbf{N_2}|}{|\mathbf{N_1}| \cdot |\mathbf{N_2}|} \] \[ = \frac{45}{9 \cdot \sqrt{29}} = \frac{5}{\sqrt{29}} \] ### Final Answer Thus, the sine of the angle formed by the lateral face ADC and the base ABC of the tetrahedron ABCD is: \[ \sin(\theta) = \frac{5}{\sqrt{29}} \]
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VIKAS GUPTA (BLACK BOOK) ENGLISH-VECTOR & 3DIMENSIONAL GEOMETRY-Exercise-5 : Subjective Type Problems
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  4. Let OABC be a tetrahedron whose edges are of unit length. If vec OA = ...

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  5. If A is the matrix [(1,-3),(-1,1)], then A-(1)/(3)A^(2)+(1)/(9)A^(3)……...

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  6. A sequence of 2xx2 matrices {M(n)} is defined as follows M(n)=[((1)/(...

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  7. Let |veca|=1, |vecb|=1 and |veca+vecb|=sqrt(3). If vec c be a vector ...

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  8. Let vecr=(veca xx vecb)sinx+(vecb xx vec c)cosy+2(vec c xx vec a), whe...

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  9. The plane denoted by P1 : 4x+7y+4z+81=0 is rotated through a right ang...

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  10. ABCD is a regular tetrahedron, A is the origin and B lies on x-axis. A...

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  11. A, B, C, D are four points in the space and satisfy |vec(AB)|=3, |vec(...

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  12. Let OABC be a regular tetrahedron of edge length unity. Its volume be ...

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  13. If veca and vecb are non zero, non collinear vectors and veca(1)=lamb...

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  14. Let P and Q are two points on the curve y=log((1)/(2))(x-0.5)+log2sqrt...

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  15. Let P and Q are two points on the curve y=log((1)/(2))(x-0.5)+log2sqrt...

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  16. If a, b, c, l, m, n in R-{0} such that al+bm+cn=0, bl+cm+an=0, cl+am+b...

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  17. Let vec ua n d vec v be unit vectors such that vec uxx vec v+ vec u=...

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