Math Problem Statement

(a) Let P = (2, 0, 1), Q = (3, 1, 0) and R = (4, 3, 5). Calculate the projection of the vector −→ P R onto the vector −→P Q

Solution

Let's calculate the projection of vector PR\overrightarrow{PR} onto vector PQ\overrightarrow{PQ}.

Given points:

  • P=(2,0,1)P = (2, 0, 1)
  • Q=(3,1,0)Q = (3, 1, 0)
  • R=(4,3,5)R = (4, 3, 5)

Step 1: Find vectors PQ\overrightarrow{PQ} and PR\overrightarrow{PR}.

Vector PQ\overrightarrow{PQ}:

PQ=QP=(3,1,0)(2,0,1)=(32,10,01)=(1,1,1)\overrightarrow{PQ} = Q - P = (3, 1, 0) - (2, 0, 1) = (3 - 2, 1 - 0, 0 - 1) = (1, 1, -1)

Vector PR\overrightarrow{PR}:

PR=RP=(4,3,5)(2,0,1)=(42,30,51)=(2,3,4)\overrightarrow{PR} = R - P = (4, 3, 5) - (2, 0, 1) = (4 - 2, 3 - 0, 5 - 1) = (2, 3, 4)

Step 2: Calculate the projection of PR\overrightarrow{PR} onto PQ\overrightarrow{PQ}.

The formula for the projection of vector a\mathbf{a} onto vector b\mathbf{b} is: Projba=abbbb\text{Proj}_{\mathbf{b}} \mathbf{a} = \frac{\mathbf{a} \cdot \mathbf{b}}{\mathbf{b} \cdot \mathbf{b}} \mathbf{b} Here, a=PR\mathbf{a} = \overrightarrow{PR} and b=PQ\mathbf{b} = \overrightarrow{PQ}.

Step 3: Compute the dot products.

PRPQ=(2,3,4)(1,1,1)=(2×1)+(3×1)+(4×1)=2+34=1\overrightarrow{PR} \cdot \overrightarrow{PQ} = (2, 3, 4) \cdot (1, 1, -1) = (2 \times 1) + (3 \times 1) + (4 \times -1) = 2 + 3 - 4 = 1 PQPQ=(1,1,1)(1,1,1)=(1×1)+(1×1)+(1×1)=1+1+1=3\overrightarrow{PQ} \cdot \overrightarrow{PQ} = (1, 1, -1) \cdot (1, 1, -1) = (1 \times 1) + (1 \times 1) + (-1 \times -1) = 1 + 1 + 1 = 3

Step 4: Calculate the projection.

ProjPQPR=13PQ=13(1,1,1)\text{Proj}_{\overrightarrow{PQ}} \overrightarrow{PR} = \frac{1}{3} \overrightarrow{PQ} = \frac{1}{3} (1, 1, -1) ProjPQPR=(13,13,13)\text{Proj}_{\overrightarrow{PQ}} \overrightarrow{PR} = \left( \frac{1}{3}, \frac{1}{3}, -\frac{1}{3} \right)

Thus, the projection of PR\overrightarrow{PR} onto PQ\overrightarrow{PQ} is (13,13,13)\left( \frac{1}{3}, \frac{1}{3}, -\frac{1}{3} \right).

Would you like further clarification or details on any step?

Here are five related questions:

  1. How do you calculate the angle between two vectors?
  2. What is the geometric interpretation of a vector projection?
  3. How can you find the magnitude of a projected vector?
  4. How does the dot product relate to the cosine of the angle between two vectors?
  5. What are the conditions for two vectors to be orthogonal?

Tip: Always double-check vector subtraction when calculating the initial direction vectors to avoid errors.

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Math Problem Analysis

Mathematical Concepts

Vector Algebra
Vector Projection
Dot Product

Formulas

Vector Projection: Proj_b(a) = (a · b / b · b) * b
Dot Product: a · b = a_x * b_x + a_y * b_y + a_z * b_z

Theorems

Dot Product Theorem
Projection Formula

Suitable Grade Level

Grades 10-12