Precalculus : Geometric Vectors

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #21 : Geometric Vectors

Subtract:  \(\displaystyle \left \langle3, 4 \right \rangle - \left \langle -4,-3\right \rangle\)

Possible Answers:

\(\displaystyle \left \langle 7,-7\right \rangle\)

\(\displaystyle \left \langle 1,-1\right \rangle\)

\(\displaystyle \left \langle 7,7\right \rangle\)

\(\displaystyle \left \langle -7,7\right \rangle\)

\(\displaystyle \left \langle -1,1\right \rangle\)

Correct answer:

\(\displaystyle \left \langle 7,7\right \rangle\)

Explanation:

Subtract the first value of the first vector, and the second value of the first vector with the second value of the second vector.

\(\displaystyle \left \langle3, 4 \right \rangle - \left \langle -4,-3\right \rangle = \left \langle 3-(-4),4-(-3)\right \rangle\)

Double negative signs are converted to a positive sign.

\(\displaystyle \left \langle 3-(-4),4-(-3)\right \rangle = \left \langle 7,7\right \rangle\)

Example Question #21 : Evaluate Geometric Vectors

Simplify:  \(\displaystyle \left \langle 2,-3,4\right \rangle+\left \langle-3,-3 \right \rangle-\left \langle5 \right \rangle\)

Possible Answers:

\(\displaystyle \left \langle -1,0,-1\right \rangle\)

\(\displaystyle \left \langle -1,-6,-1\right \rangle\)

\(\displaystyle \left \langle -8\right \rangle\)

\(\displaystyle \textup{ Cannot be solved.}\)

\(\displaystyle \left \langle -6,-6,4\right \rangle\)

Correct answer:

\(\displaystyle \textup{ Cannot be solved.}\)

Explanation:

The dimensions of the vectors are not the same.  Placeholders cannot be added to a vector.  Therefore, the values of the vectors cannot be added.

The correct answer is:  \(\displaystyle \textup{ Cannot be solved.}\)

Example Question #21 : Geometric Vectors

Find the norm of the vector \(\displaystyle \vec{v}=[2,4,3]\).

Possible Answers:

\(\displaystyle \left | \vec{v}\right |= \sqrt{29}\approx 5.385\)

\(\displaystyle \left | \vec{v}\right |= 2\sqrt{6}\approx 4.899\)

\(\displaystyle \left | \vec{v}\right |= \sqrt{9} = 3\)

\(\displaystyle \left | \vec{v}\right |= 9\)

Correct answer:

\(\displaystyle \left | \vec{v}\right |= \sqrt{29}\approx 5.385\)

Explanation:

We find the norm of a vector by finding the sum of each element squared and then taking the square root.

\(\displaystyle \left | \vec{v} \right |= \sqrt{2^2+4^2+3^2}=\sqrt{29}\).

 

Example Question #22 : Geometric Vectors

Find the norm of the vector \(\displaystyle \vec{r}=7\hat{i} +4 \hat{j}+5 \hat{k}\).

Possible Answers:

\(\displaystyle \left | \vec{r}\right | = 4\)

\(\displaystyle \left | \vec{r}\right | = 2 \sqrt{13}\)

\(\displaystyle \left | \vec{r} \ \right | = 3 \sqrt{10}\)

\(\displaystyle \left | \vec{r}\right | = 16\)

Correct answer:

\(\displaystyle \left | \vec{r} \ \right | = 3 \sqrt{10}\)

Explanation:

We find the norm of a vector by finding the sum of each component squared and then taking the square root of that sum.

\(\displaystyle \left | \vec{r}\right | = \sqrt{ 7^2+4^2+5^2 } = \sqrt{ 90 } = 3 \sqrt{10}\)

Example Question #23 : Geometric Vectors

Find the norm of the vector: \(\displaystyle < 3,-12,5.6,2,-9>\)

Possible Answers:

\(\displaystyle \sqrt{184.36}\approx 13.58\)

\(\displaystyle \sqrt{31.6}\approx 5.62\)

\(\displaystyle \sqrt{269.36}\approx 16.41\)

\(\displaystyle 31.6\)

\(\displaystyle 269.36\)

Correct answer:

\(\displaystyle \sqrt{269.36}\approx 16.41\)

Explanation:

The norm of a vector is also known as the length of the vector. The norm is given by the formula: 

\(\displaystyle \sqrt{\sum_{i=1}^nv_i^2}=\left \| v\right \|\).

Here, we have

\(\displaystyle \left \|v \right \|=\sqrt{3^2+(-12)^2+5.6^2+2^2+(-9)^2}=\sqrt{269.36}\),

the correct answer.

Example Question #23 : Geometric Vectors

Find the norm of vector \(\displaystyle \left \langle -2,2\right \rangle\).

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 0\)

\(\displaystyle \frac{1}{4}\)

\(\displaystyle 2\sqrt2\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 2\sqrt2\)

Explanation:

Write the formula to find the norm, or the length the vector.

\(\displaystyle \left \| v\right \|=\sqrt{a_{1}^2+b_{2}^2}\)

Substitute the known values of the vector and solve.

\(\displaystyle \left \| v\right \|=\sqrt{(-2)^2+2^2}= \sqrt{4+4}=\sqrt8=2\sqrt2\)

Example Question #26 : Evaluate Geometric Vectors

Find the norm (magnitude) of the following vector:

\(\displaystyle \vec{b}=3i+5j-6k\)

Possible Answers:

\(\displaystyle 70\)

\(\displaystyle \sqrt{72}\)

\(\displaystyle \sqrt{70}\)

\(\displaystyle -\sqrt{70}\)

\(\displaystyle 36\)

Correct answer:

\(\displaystyle \sqrt{70}\)

Explanation:

Use the following equation to find the magnitude of a vector:

\(\displaystyle \left \| \vec{b}\right \|=\sqrt{i^2+j^2+k^2}\)

In this case we have:

\(\displaystyle \vec{b}=3i+5j-6k\)

So plug in our values:

\(\displaystyle \left \| \vec{b}\right \|=\sqrt{3^2+5^2+(-6)^2}=\sqrt{70}\)

So:

\(\displaystyle \left \| \vec{b} \right \|=\sqrt{70}\)

Example Question #24 : Geometric Vectors

Find the product of the vector \(\displaystyle \vec{r}= 11\hat{i}+7\hat{j}\) and the scalar \(\displaystyle a=4\).

Possible Answers:

\(\displaystyle a\vec{r}=72\)

\(\displaystyle a\vec{r}=44 \hat{j}+28\vec{i}\)

\(\displaystyle a\vec{r}=44 \hat{i}+28\vec{j}\)

\(\displaystyle a\vec{r}=72 \hat{i}\)

Correct answer:

\(\displaystyle a\vec{r}=44 \hat{i}+28\vec{j}\)

Explanation:

When multiplying a vector by a scalar we multiply each component of the vector by the scalar and the result is a vector:

\(\displaystyle a \vec{r}= 4 \cdot (11 \hat{i} + 7 \hat{j}) = 44 \hat{i}+28 \hat{j}\)

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