Math Problem Statement

Find the distance the point P(8,-5,0) is to the line through the two points Q(4,-3,2), and R(6,-6,3).

Solution

To find the distance from the point P(8,5,0)P(8, -5, 0) to the line through points Q(4,3,2)Q(4, -3, 2) and R(6,6,3)R(6, -6, 3), we need to use the formula for the distance between a point and a line in 3D space.

Step-by-Step Solution:

  1. Find the direction vector of the line:

    The direction vector v\mathbf{v} of the line through points QQ and RR is given by: v=QR=(RxQx,RyQy,RzQz)\mathbf{v} = \overrightarrow{QR} = (R_x - Q_x, R_y - Q_y, R_z - Q_z)

    Substituting the coordinates of Q(4,3,2)Q(4, -3, 2) and R(6,6,3)R(6, -6, 3):

    v=(64,6+3,32)=(2,3,1)\mathbf{v} = (6 - 4, -6 + 3, 3 - 2) = (2, -3, 1)

  2. Find the vector from point QQ to point PP:

    The vector u\mathbf{u} from point QQ to point PP is:

    u=QP=(PxQx,PyQy,PzQz)\mathbf{u} = \overrightarrow{QP} = (P_x - Q_x, P_y - Q_y, P_z - Q_z)

    Substituting the coordinates of P(8,5,0)P(8, -5, 0) and Q(4,3,2)Q(4, -3, 2):

    u=(84,5+3,02)=(4,2,2)\mathbf{u} = (8 - 4, -5 + 3, 0 - 2) = (4, -2, -2)

  3. Compute the cross product of u\mathbf{u} and v\mathbf{v}:

    The cross product u×v\mathbf{u} \times \mathbf{v} is:

    \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 4 & -2 & -2 \\ 2 & -3 & 1 \end{vmatrix}$$ Calculating the determinant: $$\mathbf{u} \times \mathbf{v} = \mathbf{i} \left( (-2)(1) - (-2)(-3) \right) - \mathbf{j} \left( (4)(1) - (-2)(2) \right) + \mathbf{k} \left( (4)(-3) - (-2)(2) \right)$$ Simplifying: $$\mathbf{u} \times \mathbf{v} = \mathbf{i} \left( -2 - 6 \right) - \mathbf{j} \left( 4 + 4 \right) + \mathbf{k} \left( -12 + 4 \right)$$ $$\mathbf{u} \times \mathbf{v} = \mathbf{i} (-8) - \mathbf{j} (8) + \mathbf{k} (-8)$$ $$\mathbf{u} \times \mathbf{v} = (-8, -8, -8)$$
  4. Find the magnitude of the cross product:

    The magnitude of u×v\mathbf{u} \times \mathbf{v} is:

    u×v=(8)2+(8)2+(8)2\left| \mathbf{u} \times \mathbf{v} \right| = \sqrt{(-8)^2 + (-8)^2 + (-8)^2}

    u×v=64+64+64=192=83\left| \mathbf{u} \times \mathbf{v} \right| = \sqrt{64 + 64 + 64} = \sqrt{192} = 8\sqrt{3}

  5. Find the magnitude of the direction vector v\mathbf{v}:

    The magnitude of v=(2,3,1)\mathbf{v} = (2, -3, 1) is:

    v=22+(3)2+12\left| \mathbf{v} \right| = \sqrt{2^2 + (-3)^2 + 1^2}

    v=4+9+1=14\left| \mathbf{v} \right| = \sqrt{4 + 9 + 1} = \sqrt{14}

  6. Compute the distance from point PP to the line:

    The distance dd from point PP to the line is given by:

    d=u×vvd = \frac{\left| \mathbf{u} \times \mathbf{v} \right|}{\left| \mathbf{v} \right|}

    Substituting the values:

    d=8314d = \frac{8\sqrt{3}}{\sqrt{14}}

    Simplify by rationalizing the denominator:

    d=831414=84214=4427d = \frac{8\sqrt{3} \cdot \sqrt{14}}{14} = \frac{8\sqrt{42}}{14} = \frac{4\sqrt{42}}{7}

Final Answer:

The distance from point P(8,5,0)P(8, -5, 0) to the line through points Q(4,3,2)Q(4, -3, 2) and R(6,6,3)R(6, -6, 3) is:

4427\boxed{\frac{4\sqrt{42}}{7}}

Would you like more details on any step, or do you have any questions?


Related Questions:

  1. How do you compute the cross product of two vectors?
  2. What is the formula for finding the distance from a point to a line in 3D space?
  3. How do you find the direction vector of a line given two points?
  4. What are some practical applications of finding the distance from a point to a line?
  5. How can the cross product be used in physics and engineering?

Tip: When solving distance problems, understanding vector operations like dot and cross products is essential.

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Math Problem Analysis

Mathematical Concepts

Vector Geometry
Distance in 3D Space
Cross Product

Formulas

Distance from a point to a line in 3D: d = |u × v| / |v|
Direction vector formula: v = (Rx - Qx, Ry - Qy, Rz - Qz)
Cross product of two vectors
Magnitude of a vector: |v| = √(x^2 + y^2 + z^2)

Theorems

Cross Product Theorem
Vector Magnitude Theorem

Suitable Grade Level

Grade 11-12, College Level