Math Problem Statement

Assume that u⋅v=1 , |u|=3 , and |v|=6 .

What is the value of 2u⋅(2u−2v) ?

Solution

Given that uv=1\mathbf{u} \cdot \mathbf{v} = 1, u=3|\mathbf{u}| = 3, and v=6|\mathbf{v}| = 6, we need to find the value of 2u(2u2v)2\mathbf{u} \cdot (2\mathbf{u} - 2\mathbf{v}).

We can approach this step by step:

Step 1: Expand the expression

First, expand the expression:

2u(2u2v)=2u2u2u2v2\mathbf{u} \cdot (2\mathbf{u} - 2\mathbf{v}) = 2\mathbf{u} \cdot 2\mathbf{u} - 2\mathbf{u} \cdot 2\mathbf{v}

This simplifies to:

4(uu)4(uv)4(\mathbf{u} \cdot \mathbf{u}) - 4(\mathbf{u} \cdot \mathbf{v})

Step 2: Substitute known values

Now, substitute the given values:

  • uu=u2=32=9\mathbf{u} \cdot \mathbf{u} = |\mathbf{u}|^2 = 3^2 = 9
  • uv=1\mathbf{u} \cdot \mathbf{v} = 1

Substituting these into the expression:

4(9)4(1)=364=324(9) - 4(1) = 36 - 4 = 32

Final Answer

The value of 2u(2u2v)2\mathbf{u} \cdot (2\mathbf{u} - 2\mathbf{v}) is 32\boxed{32}.

Do you want details or have any questions?

Here are some related questions:

  1. What is the angle between vectors u\mathbf{u} and v\mathbf{v}?
  2. How would the result change if u=2|\mathbf{u}| = 2 instead?
  3. Can you find the value of u+v\mathbf{u} + \mathbf{v} using the given information?
  4. What is the geometric interpretation of the dot product in this context?
  5. How do you calculate the projection of u\mathbf{u} onto v\mathbf{v}?

Tip: Always check if vectors are perpendicular by verifying if their dot product is zero.

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Math Problem Analysis

Mathematical Concepts

Vector Algebra
Dot Product
Vector Magnitude

Formulas

Dot Product: u⋅v = |u||v|cos(θ)
Magnitude of a Vector: |u| = sqrt(u_x^2 + u_y^2 + u_z^2)
Expansion of Dot Product: u⋅(v + w) = u⋅v + u⋅w

Theorems

Distributive Property of the Dot Product

Suitable Grade Level

Grades 10-12