3D Geometry: Planes and Angles

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Questions and Answers

If two planes, defined by their normal vectors $\overrightarrow{n_1}$ and $\overrightarrow{n_2}$, are parallel, what is the relationship between their normal vectors?

  • $\overrightarrow{n_1} \cdot \overrightarrow{n_2} = 0$
  • $\overrightarrow{n_1} \cdot \overrightarrow{n_2} = 1$
  • $\overrightarrow{n_1} = \overrightarrow{n_2} = 0$
  • $\overrightarrow{n_1} = \lambda \overrightarrow{n_2}$ (correct)

If two planes, $ax + by + cz + d = 0$ and $a'x + b'y + c'z + d' = 0$, are perpendicular, what condition must be met by their coefficients?

  • $aa' + bb' + cc' + dd' = 0$
  • $\frac{a}{a'} = \frac{b}{b'} = \frac{c}{c'}$
  • $\frac{a}{a'} + \frac{b}{b'} + \frac{c}{c'} = 0$
  • $aa' + bb' + cc' = 0$ (correct)

In three-dimensional space, what geometric object does the equation $2y + 3z = 0$ represent?

  • None of these
  • A plane passing through the X-axis (correct)
  • A plane passing through the Y-axis
  • A plane passing through the Z-axis

What is the condition for the line $\frac{x-x_1}{a_1} = \frac{y-y_1}{b_1} = \frac{z-z_1}{c_1}$ to be parallel to the plane $ax + by + cz + d = 0$?

<p>$aa_1 + bb_1 + cc_1 = 0$ (B)</p> Signup and view all the answers

If the angle between the normal to the planes is $\frac{\pi}{2}$, what can be concluded?

<p>$\overrightarrow{n_1} \cdot \overrightarrow{n_2} = 0$ (D)</p> Signup and view all the answers

Two planes are given by their normal vectors $\overrightarrow{n_1}$ and $\overrightarrow{n_2}$. What does $\overrightarrow{n_1} \cdot \overrightarrow{n_2} = 0$ imply?

<p>The planes are orthogonal. (C)</p> Signup and view all the answers

Which of the following represents the equation of a plane?

<p>$ax + by + cz = d$ (C)</p> Signup and view all the answers

What does the equation $\frac{x-x_0}{a} = \frac{y-y_0}{b} = \frac{z-z_0}{c}$ represent?

<p>A line (D)</p> Signup and view all the answers

What is a normal vector to the plane $ax + by + cz + d = 0$?

<p>$&lt;a, b, c&gt;$ (D)</p> Signup and view all the answers

What is the dot product of two orthogonal vectors?

<p>0 (D)</p> Signup and view all the answers

If a line is perpendicular to a plane, how is its direction vector related to the plane's normal vector?

<p>They are parallel. (A)</p> Signup and view all the answers

If two vectors are parallel, what is the angle between them?

<p>$0$ (D)</p> Signup and view all the answers

What is the general form of a linear equation in three-dimensional space?

<p>$ax + by + cz = d$ (D)</p> Signup and view all the answers

What does the cross product of two vectors result in?

<p>A vector (A)</p> Signup and view all the answers

What is the relationship between a plane's normal vector and any vector lying in the plane?

<p>Perpendicular (A)</p> Signup and view all the answers

If the dot product of two vectors is zero, what can be said about the angle between them?

<p>They are perpendicular (B)</p> Signup and view all the answers

Which of the following is a vector equation of a line?

<p>$r = r_0 + tv$ (A)</p> Signup and view all the answers

A line is defined by a point and a direction vector. What does the direction vector indicate?

<p>The orientation of the line (D)</p> Signup and view all the answers

Given a point $(x_0, y_0, z_0)$ and a normal vector $\mathbf{n} = \langle a, b, c \rangle$, what is the general equation of a plane?

<p>$a(x - x_0) + b(y - y_0) + c(z - z_0) = 0$ (A)</p> Signup and view all the answers

What is the value of $k$ such that the point $(x, 4, -4)$ lies in the plane $2x - 4y + z = 7$?

<p>No real value (C)</p> Signup and view all the answers

Flashcards

Angle between Planes

The angle between two planes is the angle between their normal vectors.

Parallel Planes

If two planes are parallel, their normal vectors are parallel (scalar multiples of each other).

Perpendicular Planes

If two planes are perpendicular, the dot product of their normal vectors is zero.

Plane Equation 2y + 3z = 0

A plane in the form 2y + 3z = 0 passes through the X-axis.

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Angle between Line and Plane

To find the angle between a line and a plane, use the formula involving the dot product of the direction vector of the line and the normal vector of the plane.

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Line Parallel to Plane Condition

A line defined by (x-x1)/a = (y-y1)/b = (z-z1)/c is parallel to the plane ax + by + cz + d = 0 if aa1 + bb1 + cc1 = 0.

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Study Notes

  • Equation of a plane passing through a point and parallel to a plane is given.
  • Equation of a plane through the origin and passing through a line is described.
  • The equation of the perpendicular from a point to the plane ax + by + cz + d = 0 is given.
  • Equation of a line passing through point (1, 1, 1) and parallel to the plane 2x + 3y + z + 5 = 0 is described.
  • If planes ax + by + cz + d = 0 and a'x + b'y + c'z + d' = 0 are perpendicular, then aa' + bb' + cc' = 0.
  • In space, 2y + 3z = 0 represents a plane passing through the X-axis.

Angles

  • The acute angle between the line r = (3i - j - k) + λ(i - j + k) and the plane r • (i - 4k) = 4 is cos⁻¹(1/√3).
  • The angle between two planes r·(2i - j + k) = 6 and r·(i + j + 2k) = 5 is π/3.
  • Two planes r·n₁ = p₁ and r·n₂ = p₂ are parallel if n₁ = λn₂.
  • If the angle between the normal to the planes is π/2, then n₁ • n₂ = 0.
  • The angle between the line x/3 = y/2 = z/2 and the plane 3x + 2y - 3z = 4 is 45°.
  • The angle between the line (x+1)/-3 = (y-1)/2 = (z-2)/4 and the plane 2x + y - 3z + 4 = 0 is 30°.
  • To find the angle between the plane ax + by + cz + d = 0 and the line (x-1)/a = (y-2)/b = (z-3)/c.
  • The angle between the line 6x = 4y = 3z and the plane 3x + 2y - 3z = 4 is 90°.
  • The line (x-x₁)/a₁ = (y-y₁)/b₁ = (z-z₁)/c₁ is parallel to the plane ax + by + cz + d = 0 if aa₁ + bb₁ + cc₁ = 0.

Values

  • The value of k such that (x-4)/2 = (y-k)/1 = (z-2)/2 lies in the plane 2x - 4y + z = 7, is no real value.
  • The angle between two planes x + 2y + 2z = 3 and -5x + 3y + 4z = 9 is cos⁻¹(¹⁰/√2).
  • The angle between the line (x-2)/1 = (y-1)/2 = (z+1)/3 and the plane r • (2i - j + k) = 4 is sin⁻¹(¹/√6).
  • Equation of a line passing through (1, 2, 3) and perpendicular to the YZ-plane is y-2 = 0, z-3 = 0.
  • The line passing through (1, 1, 1) and perpendicular to 2x - 3y + z = 5 is (x-1)/2 = (y-1)/-3 = (z-1)/1.

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