Linear Algebra : Norms

Study concepts, example questions & explanations for Linear Algebra

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Example Questions

Example Question #1 : Norms

Find the norm of the following vector.

 

\(\displaystyle A=[3,4,5]\)

Possible Answers:

\(\displaystyle \left \| A\right \|=\sqrt{2}\)

\(\displaystyle \left \| A\right \|=5\)

\(\displaystyle \left \| A\right \|=5\sqrt{2}\)

\(\displaystyle \left \| A\right \|=2\sqrt{5}\)

\(\displaystyle \left \| A\right \|=\sqrt{52}\)

Correct answer:

\(\displaystyle \left \| A\right \|=5\sqrt{2}\)

Explanation:

The norm of a vector is simply the square root of the sum of each component squared. 

\(\displaystyle \left \| A\right \|=\sqrt{3^2+4^2+5^2}=\sqrt{9+16+25}=\sqrt{50}=5\sqrt{2}\)

Example Question #1 : Norms

Find the norm of vector \(\displaystyle A\).

\(\displaystyle A=(\cos(x), \sin(x))\)

Possible Answers:

\(\displaystyle \left \| A\right \|=1\)

\(\displaystyle \left \| A\right \|=1+\sin^2(x)\)

\(\displaystyle \left \| A\right \|=1+\cos^2(x)\)

\(\displaystyle \left \| A\right \|=\cos(x)+\sin(x)\)

\(\displaystyle \left \| A\right \|=0\)

Correct answer:

\(\displaystyle \left \| A\right \|=1\)

Explanation:

In order to find the norm, we need to square each component, sum them up, and then take the square root.

\(\displaystyle \left \| A\right \|=\sqrt{\cos^2(x)+\sin^2(x)}=\sqrt{1}=1\)

Example Question #1 : Norms

Find the norm, \(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}\), given \(\displaystyle \bf{a}= \begin{bmatrix} 2\\ 1\\ 7\\ -2 \end{bmatrix}\)

Possible Answers:

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}=\sqrt{8}\)

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}=-28\)

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}=58\)

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}=\sqrt{58}\)

Correct answer:

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}=\sqrt{58}\)

Explanation:

By definition, 

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}= \sqrt{a_1^2+a_2^2+a_3^2+...+a_n^2}\),

therefore,

\(\displaystyle \begin{Vmatrix} \bf{a} \end{Vmatrix}= \sqrt{2^2+1^2+7^2+(-2)^2}= \sqrt{58}\).

Example Question #1 : Norms

Calculate the norm of \(\displaystyle \bf{A}\times \bf{B}\) , or \(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}\), given

\(\displaystyle \bf{A} = 3 \hat{i} - 1 \hat{j}\),

 \(\displaystyle \bf{B} = -1 \hat{k}\).

 

Possible Answers:

\(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}= 10\)

\(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}=\sqrt{10}\)

\(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}= 4\)

Can not be determined.

Correct answer:

\(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}=\sqrt{10}\)

Explanation:

First, we need to find \(\displaystyle \bf{A}\times \bf{B}\).  This is, by definition,

\(\displaystyle \bf{A \times \bf{B}}= \begin{vmatrix} \hat{i}&\hat{j} &\hat{k} \\ 3& -1& 0\\ 0&0 &-1 \end{vmatrix}= 1\hat{i}+3\hat{j}\).

Therefore, 

\(\displaystyle \begin{Vmatrix} \bf{A}\times \bf{B} \end{Vmatrix}=\sqrt{1^2+3^2}=\sqrt{10}\).

Example Question #1 : Norms

Find the norm of the vector \(\displaystyle \vec{v} = (4, 3, 0)\)

Possible Answers:

\(\displaystyle 7\)

\(\displaystyle 1\)

\(\displaystyle \sqrt{7}\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 5\)

Explanation:

To find the norm, square each component, add, then take the square root:

\(\displaystyle \sqrt{4^2 + 3^2 + 0^2 } = \sqrt{16 + 9 } = \sqrt{25 } = 5\)

Example Question #1 : Norms

Find a unit vector in the same direction as \(\displaystyle \vec{v} = (2, -3, \sqrt{3})\)

Possible Answers:

\(\displaystyle (1, -1.5, \frac{\sqrt3}{2} )\)

\(\displaystyle (\frac{1}{2} , -\frac{3}{4} , \frac{\sqrt{3}}{4})\)

\(\displaystyle (\frac{2}{\sqrt{2}}, -\frac{3}{\sqrt{2}}, \sqrt{\frac{3}{2}})\)

\(\displaystyle (4,4,4)\)

Correct answer:

\(\displaystyle (\frac{1}{2} , -\frac{3}{4} , \frac{\sqrt{3}}{4})\)

Explanation:

First, find the length of the vector: \(\displaystyle \sqrt{ 2^2 + (-3)^2 + (\sqrt{3})^2 } = \sqrt{4+9+3} = \sqrt{16} = 4\)

Because this vector has the length of 4 and a unit vector would have a length of 1, divide everything by 4:

\(\displaystyle ( \frac{ 2}{4} , \frac{-3}{4} , \frac{\sqrt{3}}{4}) = (\frac{1}{2} , -\frac{3}{4} , \frac{\sqrt{3}}{4})\)

Example Question #1 : Norms

Find the norm of the vector \(\displaystyle \vec{v} = (-1, 3, 2,2)\)

Possible Answers:

\(\displaystyle 2 \sqrt{3}\)

\(\displaystyle \sqrt{6}\)

\(\displaystyle 3\)

\(\displaystyle 3 \sqrt{2}\)

Correct answer:

\(\displaystyle 3 \sqrt{2}\)

Explanation:

\(\displaystyle || \vec{v} || = \sqrt{ (-1)^2 + 3^2 + 2^2 + 2^2 } = \sqrt{ 1 + 9 + 4 + 4 } = \sqrt{18}\)

This can be simplified:

\(\displaystyle \sqrt{18 } = \sqrt{3\cdot3\cdot2 } = 3 \sqrt{2 }\)

Example Question #1 : Norms

Find the norm of the vector \(\displaystyle \vec{v} = (2, -3, 1 )\)

Possible Answers:

\(\displaystyle \sqrt{4}\)

\(\displaystyle 0\)

\(\displaystyle \sqrt{14 }\)

\(\displaystyle \sqrt{10}\)

Correct answer:

\(\displaystyle \sqrt{14 }\)

Explanation:

\(\displaystyle || \vec{v} || = \sqrt{2^2 + (-3)^2 + 1^2 } = \sqrt{4+9+1} = \sqrt{14}\)

Example Question #2 : Norms

Find the norm of the vector \(\displaystyle \vec{v}= (4, 2, -5 )\)

Possible Answers:

\(\displaystyle 5 \sqrt{2}\)

\(\displaystyle 5\)

\(\displaystyle 9\)

\(\displaystyle 3 \sqrt{5}\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 3 \sqrt{5}\)

Explanation:

\(\displaystyle || \vec{v} || = \sqrt{ 4^2 + 2^2 + (-5)^2 } = \sqrt{16 + 4 + 25 } = \sqrt{45}\)

This can be simplified:

\(\displaystyle \sqrt{3 \cdot 3 \cdot 5 } = 3 \sqrt {5}\)

Example Question #1 : Norms

Find the norm of the vector \(\displaystyle \vec{v} = (2, -3, -6 )\)

Possible Answers:

\(\displaystyle \sqrt{23}\)

\(\displaystyle \sqrt{41 }\)

\(\displaystyle 7\)

\(\displaystyle 6\)

Correct answer:

\(\displaystyle 7\)

Explanation:

\(\displaystyle || \vec{v} || = \sqrt{ 2^2 + (-3)^2 + (-6)^2 } = \sqrt{4 + 9 + 36 } = \sqrt{49} = 7\)

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