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Precalculus : Algebraic Vectors and Parametric Equations

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Example Questions

Example Question #12 : Find A Direction Vector When Given Two Points

If $\overrightarrow{DE}=<5, -1>$ and E=(-2, -1) , which of the following is a possible point for ?

Possible Answers:

(0, -3)

(-3, -2)

(-7,0)

(3, -2)

Correct answer:

(-7,0)

Explanation:

To find the directional vector, subtract the coordinates of the initial point from the coordinates of the terminal point.

To find the x-coordinate of ,

-2-x=5

x=-7

To find the y-coordinate of ,

-1-y=-1

y=0

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Example Question #11 : Find A Direction Vector When Given Two Points

If $\overrightarrow{EF}=<2, -8>$ and E=(-1, 5) , what is one possible point for ?

Possible Answers:

(1, -3)

(-3, -3)

(3, 3)

(-3, 3)

Correct answer:

(1, -3)

Explanation:

To find the directional vector, subtract the coordinates of the initial point from the coordinates of the terminal point.

To find the x-coordinate of ,

x-(-1)=2

x=1

To find the y-coordinate of ,

y-5=-8

y=-3

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Example Question #12 : Find A Direction Vector When Given Two Points

If $\overrightarrow{OP}=<4, -2>$ and O=(2, 10) , what is a possible value of ?

Possible Answers:

(-6, 8)

(6, -2)

(6, 8)

(8, 6)

Correct answer:

(6, 8)

Explanation:

To find the directional vector, subtract the coordinates of the initial point from the coordinates of the terminal point.

To find the x-coordinate of ,

x-2=4

x=6

To find the y-coordinate of ,

y-10=-2

y=8

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Example Question #1 : Express A Vector In Polar Form

Rewrite the vector $\vec{v}= 3 \hat{i} + 5 \hat{j}$ from Cartesian coordinates to polar coordinates $\vec{v} = \left \langle r \angle \theta \right \rangle$ .

Possible Answers:

$\vec{v} = \left \langle \sqrt{21} \angle 32.64^\circ \right \rangle$

$\vec{v} = \left \langle \sqrt{8} \angle 60^\circ \right \rangle$

$\vec{v} = \left \langle 16 \angle 60^\circ \right \rangle$

$\vec{v} = \left \langle \sqrt{34} \angle 59.04^\circ \right \rangle$

Correct answer:

$\vec{v} = \left \langle \sqrt{34} \angle 59.04^\circ \right \rangle$

Explanation:

To convert to polar form, we need to find the magnitude of the vector, , and the angle it forms with the positive -axis going counterclockwise, or $\theta$ . This is shown in the figure below.

Vecfssec

We find the angle using trigonometric identities:

$\tan{\theta}= \frac{5}{3}$

Using a calculator,

$\theta = \arctan{\frac{5}{3}} \approx 59.04^\circ$

To find the magnitude of a vector, we add up the squares of each component and take the square root:

$r= \left | \vec{v}\right | = \sqrt{3^2+5^2}=\sqrt{34}$ .

So, our vector written in polar form is

$\vec{v} = \left \langle \sqrt{34} \angle 59.04^\circ \right \rangle$

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Example Question #1 : Express A Vector In Polar Form

Express the vector $\left \langle 1,-1\right \rangle$ in polar form.

Possible Answers:

$\left(1, -\frac{\pi}{4}\right)$

$\left(\sqrt2, -\frac{3\pi}{4}\right)$

$\left(\sqrt2, \frac{3\pi}{4}\right)$

$\left(\sqrt2, -\frac{\pi}{4}\right)$

$\left(\frac{\sqrt2}{2}, \frac{3\pi}{4}\right)$

Correct answer:

$\left(\sqrt2, -\frac{\pi}{4}\right)$

Explanation:

To convert a point or a vector to its polar form, use the following equations to determine the magnitude and the direction.

$M=\sqrt{x^2+y^2}$

$\theta=tan^-^1 (\frac{y}{x})$

Substitute the vector $\left \langle 1,-1\right \rangle$ to the equations to find the magnitude and the direction.

$M=\sqrt{(1)^2+(-1)^2}= \sqrt2$

$\theta=tan^-^1 (\frac{-1}{1}) = tan^-^1 (-1) = -\frac{\pi}{4}$

The polar form is: $(M,\theta)= (\sqrt2, -\frac{\pi}{4})$

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Example Question #2 : Express A Vector In Polar Form

Express $\left \langle 3,6\right \rangle$ in polar form in degrees.

Possible Answers:

(18,1.107)

(9,63.434)

$(9,\frac{\pi}{2})$

$(\sqrt{45},63.435)$

$(\sqrt{45},1.107)$

Correct answer:

$(\sqrt{45},63.435)$

Explanation:

The polar form of the vector is: $(R,\theta)$

Find .

$R=\sqrt{ x^2+ y^2}=\sqrt{ 3^2+ 6^2}=\sqrt{9+36}=\sqrt{45}$

Find the angle.

$\theta= tan^-^1\left(\frac{y}{x}\right)= tan^-^1\left(\frac{6}{3}\right)=63.435$

$(R,\theta)=(\sqrt{45},63.435)$

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Example Question #21 : Algebraic Vectors And Parametric Equations

Express the vector in polar form.

v=<3,15>

Possible Answers:

$v\approx(15.30,78.69^o)$

$v\approx(3.06,11.31^o)$

$v\approx(3.00,0.0035)$

$v\approx(3.059,78.69^o)$

Correct answer:

$v\approx(15.30,78.69^o)$

Explanation:

We know that converting into polar form requires using the formulas : $x=r\cos\theta$ and $y=r\sin\theta$ .

Solving for r will give us the equation:

$r=\frac{x}{\cos\theta}=\frac{y}{sin\theta}$

We can then solve this equation for theta thusly:

$\frac{y}{x}=\frac{sin\theta}{\cos\theta}\implies\tan^{-1}\left(\frac{x}{y}\right)=\theta$

We substitute the values of x and y found in the vector equation to get the angle measure:

$\theta=\tan^{-1}\left(\frac{15}{3}\right)\approx78.69^o$

Since we have already solved for the radius in terms of x and y and the angle, we substitute the proper values into the equation to get the radius.

$r=\frac{x}{\cos\theta}=\frac{3}{\cos78.69^o}\approx15.30$

Therefore, the vector expressed in polar form is:

v=(15.30,78,69^o)

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Example Question #21 : Algebraic Vectors And Parametric Equations

Write the following vector in polar form: $\left \langle -3,-2\right \rangle$

Possible Answers:

$(\sqrt{13},33.69)$

(4,-33.69)

$\left(4,\frac{\pi}{3}\right)$

$(\sqrt{13},213.69)$

(13,213.69)

Correct answer:

$(\sqrt{13},213.69)$

Explanation:

To find the polar form of $\left \langle -3,-2\right \rangle$ , two formula will be needed since the polar form of a vector is defined as $(r,\theta)$ .

$r=\sqrt{x^2+y^2}$

$tan(\theta) = \frac{y}{x}$

$r=\sqrt{x^2+y^2}=\sqrt{(-3)^2+(-2)^2}=\sqrt{13}$

$\theta = tan^-^1(\frac{-2}{-3}) =33.69$

However, the direction of $\left \langle -3,-2\right \rangle$ is not in the first quadrant, but lies in the third quadrant. It is mandatory to add 180 degrees so that the angle corresponds to the correct quadrant.

$\theta = 33.69+180 = 213.69$

Therefore, the answer is:

$(r,\theta)= (\sqrt{13},213.69 )$

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Example Question #1 : Express A Vector In Polar Form

Write this vector in component form:

Vector 1

Possible Answers:

$\small <7.36, 8.17>$

$\small <9.16, 47.12>$

$\small <12.22, 12.22>$

$\small <8.17, 7.36>$

$\small <47.12, 9.16>$

Correct answer:

$\small <7.36, 8.17>$

Explanation:

To figure out the horizontal component, set up an equation involving cosine, since that side of the implied triangle is adjacent to the 48-degree angle:

$\small cos(48)=\frac{x}{11}$ To solve for x, first find the cosine of 48, then multiply by 11:

$\small 7.36 \approx x$

To figure out the vertical component, set up an equation involving sine, since that side of the implied triangle is opposite the 48-degree angle:

$\small sin(48)=\frac{y}{11}$ to solve for y, just like x, first find the sine of 48, then multiply by 11:

$\small 8.17 \approx y$

Putting this in component form results in the vector $\small <7.36, 8.17>$

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Example Question #1 : Express A Vector In Polar Form

Write the vector $\small <2, -7>$ in polar form $\small (r,\theta)$ .

Possible Answers:

$\small (\sqrt{45}, 74.05^o)$

$\small (\sqrt{53}, 105.95^o)$

$\small (\sqrt{53}, 285.95^o)$

$\small (\sqrt{45}, 285.95^o)$

$\small (\sqrt{53}, 74.05^o)$

Correct answer:

$\small (\sqrt{53}, 285.95^o)$

Explanation:

First, it could be helpful to draw the vector so that we can get a sense of what it looks like. The component form $\small <2, -7>$ means from the start to the end, it moves forward 2 and down 7:

Vector 3

We can now use the Pythagorean Theorem to solve for the magnitude:

$\small 2^2 + 7^2 = C^2$ note that if you had used -7 that would be perfect as well, since that would give you the exact same answer.

$\small 4 + 49 = C^2$

$\small 53 = C^2$ take the square root of both sides

$\small \sqrt{53}= C$ The magnitude is $\small \sqrt{53}$ .

Now to find the angle we should use trigonometric ratios. We can consider the angle being formed by the vector and the component 2, then we can place it in the right quadrant later on. We know that the tangent of that angle is $\small \frac{7}{2}$ :

$\small tan(\theta)= \frac{7}{2}$ now we can take $\small tan^{-1}$ of both sides to determine theta:

$\small \theta \approx 74.05^o$

We can see that the angle for this particular vector is pointing down and to the right, so the angle we want is in the 4th quadrant. This angle would be $\small 360^o - 74.05^o = 285.95^o$

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Precalculus : Algebraic Vectors and Parametric Equations

Study concepts, example questions & explanations for Precalculus

All Precalculus Resources

Example Questions

Example Question #12 : Find A Direction Vector When Given Two Points

Example Question #11 : Find A Direction Vector When Given Two Points

Example Question #12 : Find A Direction Vector When Given Two Points

Example Question #1 : Express A Vector In Polar Form

Example Question #1 : Express A Vector In Polar Form

Example Question #2 : Express A Vector In Polar Form

Example Question #21 : Algebraic Vectors And Parametric Equations

Example Question #21 : Algebraic Vectors And Parametric Equations

Example Question #1 : Express A Vector In Polar Form

Example Question #1 : Express A Vector In Polar Form

All Precalculus Resources

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