Calculus 3 : Vectors and Vector Operations

Study concepts, example questions & explanations for Calculus 3

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Example Questions

Example Question #441 : Vectors And Vector Operations

Find the dot product between the vectors \(\displaystyle \left \langle 3,10,5\right \rangle\) and \(\displaystyle \left \langle 1,2,6\right \rangle\)

Possible Answers:

\(\displaystyle 53\)

\(\displaystyle 60\)

\(\displaystyle \left \langle 3,20,30\right \rangle\)

\(\displaystyle 52\)

Correct answer:

\(\displaystyle 53\)

Explanation:

The formula for the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) is \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors from the problem statement, we get \(\displaystyle (3*1)+(10*2)+(6*5)=53\)

Example Question #441 : Vectors And Vector Operations

Solve:

\(\displaystyle \left \langle \sec(z), 14\right \rangle \cdot \left \langle 3, \tan(z)\right \rangle\)

Possible Answers:

\(\displaystyle \left \langle 3\sec(z), 14\tan(z) \right \rangle\)

\(\displaystyle \sec(z)+\tan(z)\)

\(\displaystyle 3\sec(z)+14\tan(z)\)

\(\displaystyle 42\sec(z)\tan(z)\)

Correct answer:

\(\displaystyle 3\sec(z)+14\tan(z)\)

Explanation:

The dot product of two vectors is given by the sum of the products of the corresponding components (for example, \(\displaystyle \left \langle a, b\right \rangle \cdot \left \langle x, y\right \rangle=ax+by\))

Our final answer is

\(\displaystyle 3\sec(z)+14\tan(z)\)

Example Question #128 : Dot Product

Find the dot product between \(\displaystyle \left \langle 1,-4,5\right \rangle\) and \(\displaystyle \left \langle 2,2,1\right \rangle\)

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle \left \langle 2,-8,5\right \rangle\)

\(\displaystyle 3\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle -1\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (1*2)+(-4*2)+(5*1)=-1\)

Example Question #129 : Dot Product

Find the dot product between \(\displaystyle \left \langle \sin(x),y,5\right \rangle\) and \(\displaystyle \left \langle \csc(x),2,4\right \rangle\)

Possible Answers:

\(\displaystyle 4y+20\)

\(\displaystyle 3y+22\)

\(\displaystyle 2y+21\)

\(\displaystyle y+5\)

Correct answer:

\(\displaystyle 2y+21\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (\sin(x)*\csc(x))+(y*2)+(5*4)=2y+21\)

Example Question #122 : Dot Product

Find the dot product between \(\displaystyle \left \langle x,2y,z\right \rangle\) and \(\displaystyle \left \langle 2,2,1\right \rangle\)

Possible Answers:

\(\displaystyle 2x-3y-z\)

\(\displaystyle x+3y+2z\)

\(\displaystyle x+3y-z\)

\(\displaystyle 2x+4y+z\)

Correct answer:

\(\displaystyle 2x+4y+z\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (x*2)+(2y*2)+(z*1)=2x+4y+z\)

Example Question #131 : Dot Product

Find the dot product between \(\displaystyle \left \langle 3,2y,z^5\right \rangle\) and \(\displaystyle \left \langle 3x,yz,z^2\right \rangle\)

Possible Answers:

\(\displaystyle 9x+2x^2y+z^7\)

\(\displaystyle 9x+2yz+z^7\)

\(\displaystyle 9x+2y^2z+z^7\)

\(\displaystyle 2x^2+2y^2x-z\)

Correct answer:

\(\displaystyle 9x+2y^2z+z^7\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (3*3x)+(2y*yz)+(z^5*z^2)=9x+2y^2z+z^7\)

Example Question #132 : Dot Product

Find the dot product between \(\displaystyle \left \langle 3x,4y,z\right \rangle\) and \(\displaystyle \left \langle 4,2,7\right \rangle\)

Possible Answers:

\(\displaystyle 2x+y-9z\)

\(\displaystyle 12x+8y+7z\)

\(\displaystyle 4x-3y+5z\)

\(\displaystyle x+4y-3z\)

Correct answer:

\(\displaystyle 12x+8y+7z\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (3x*4)+(4y*2)+(z*7)=12x+8y+7z\)

Example Question #133 : Dot Product

Find the dot product between \(\displaystyle \left \langle 2,-3,4\right \rangle\) and \(\displaystyle \left \langle 5,-4,1\right \rangle\)

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle 30\)

\(\displaystyle 26\)

\(\displaystyle 22\)

Correct answer:

\(\displaystyle 26\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (2*5)+(-3*-4)+(4*1)=10+12+4=26\)

Example Question #134 : Dot Product

Find the dot product between \(\displaystyle \left \langle x,-3,4z\right \rangle\) and \(\displaystyle \left \langle x,y,z\right \rangle\)

Possible Answers:

\(\displaystyle x^2+6y+4z^2\)

\(\displaystyle x^3+y+7z^2\)

\(\displaystyle x^2-5y+5z^2\)

\(\displaystyle x^2-3y+4z^2\)

Correct answer:

\(\displaystyle x^2-3y+4z^2\)

Explanation:

To find the dot product between two vectors \(\displaystyle a=\left \langle x_1,y_1,z_1\right \rangle\) and \(\displaystyle b=\left \langle x_2,y_2,z_2\right \rangle\) we use the formula \(\displaystyle a\cdot b=(x_1*x_2)+(y_1*y_2)+(z_1*z_2)\). Using the vectors in the problem statement, we get \(\displaystyle (x*x)+(-3*y)+(4z*z)=x^2-3y+4z^2\)

Example Question #131 : Dot Product

Consider the vector \(\displaystyle \mathbf{v}=\mathbf{i}+7\mathbf{j}+2\mathbf{k}\).

Which of the following vectors are orthogonal to v?

Possible Answers:

\(\displaystyle 4\mathbf{i}-2\mathbf{j}+\mathbf{k}\)

\(\displaystyle 6\mathbf{i}+-3\mathbf{j}+5\mathbf{k}\)

\(\displaystyle -4\mathbf{i}+3\mathbf{j}-2\mathbf{k}\)

\(\displaystyle -5\mathbf{i}+2\mathbf{j}+3\mathbf{k}\)

\(\displaystyle -\mathbf{i}+3\mathbf{k}\)

Correct answer:

\(\displaystyle 4\mathbf{i}-2\mathbf{j}+\mathbf{k}\)

Explanation:

Two vectors are defined as orthogonal when their dot product is zero.

 

The dot product of two vectors

 \(\displaystyle \mathbf{u}=u_x\mathbf{i}+u_y\mathbf{j}+u_z\mathbf{k}\)   and   \(\displaystyle \mathbf{v}=v_x\mathbf{i}+v_y\mathbf{j}+v_z\mathbf{k}\)

Is given by the expression:

\(\displaystyle \mathbf{u}\cdot\mathbf{v}=u_xv_x+u_yv_y+u_zv_z\)

 

The only vector that satisfies the requirement that the dot product of it and is zero is \(\displaystyle 4\mathbf{i}-2\mathbf{j}+\mathbf{k}\):

\(\displaystyle (3\mathbf{i}+7\mathbf{j}+2\mathbf{k})\cdot (4\mathbf{i}-2\mathbf{j}+\mathbf{k}) =(3)(4)+(7)(-2)+(2)(2)=12-14+2=0\)

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