Answer:
See below for answers and explanations
Step-by-step explanation:
Problem 1
First, identify the three vectors in component form (remember to have the direction angle for each vector account for the quadrants they are in!):
[tex]u=\langle90\cos220^\circ,90\sin220^\circ\rangle\\v=\langle 60\cos110^\circ,60\sin110^\circ\rangle\\w=\langle 40\cos30^\circ,40\sin30^\circ\rangle[/tex]
Secondly, we add them:
[tex]u+v+w=\langle90\cos220^\circ+60\cos110^\circ+40\cos30^\circ,90\sin220^\circ+60\sin110^\circ+40\sin30^\circ\rangle\approx\langle-54.824,18.531\rangle[/tex]
Thirdly, find the magnitude of the new vector:
[tex]||u+v+w||=\sqrt{(-54.824)^2+(18.531)^2}\\||u+v+w||\approx57.871[/tex]
And finally, find the direction of the new vector:
[tex]\theta=tan^{-1}(\frac{18.531}{-54.824})\\\theta\approx-18.675^\circ\approx-19^\circ[/tex]
Because our new vector is in Quadrant II, our found direction angle is a reference angle, telling us that the actual direction of our vector is 19° clockwise from the negative x-axis, which would be 180°-19°=161°
Thus, B is the best answer
Problem 2
To find the component form of a vector, we simply subtract the initial point from the terminal point. In this case, our initial point is at (7,-1) and our terminal point is at (1,6). We subtract the horizontal and vertical components separately:
[tex]\langle1-7,6-(-1)\rangle=\langle-6,7\rangle[/tex]
Thus, A is the correct answer
Problem 3
Again, subtract the initial point from the terminal point to find the vector, and then apply scalar multiplication:
[tex]-\frac{1}{2}v=-\frac{1}{2} \langle-8-8,10-4\rangle=-\frac{1}{2}\langle-16,6\rangle=\langle8,-3\rangle[/tex]
Thus, C is the correct answer
Problem 4 (top one in 4th image)
Remember that scalar multiplication only affects the magnitude of the vector and not the direction. Thus, [tex]-3u=-3\bigr[20\langle\cos30^\circ,\sin30^\circ\rangle\bigr]=-60\langle\cos30^\circ,\sin30^\circ\rangle[/tex], which means our magnitude is -60 and our direction remains 30°.
Thus, B is the correct answer
Problem 5 (fake #6, bottom one in 4th image)
Basically, whatever is in front of the i represents the horizontal component, and whatever is in front of the j represents the vertical component, so:
[tex]u=-3i+8j=\langle-3,8\rangle[/tex]
Thus, B is the correct answer
Problem 6 (real one, 5th image)
Recall:
- Two vectors are said to be orthogonal if their dot product is 0 and are perpendicular to each other (form a 90° angle)
- Two vectors are said to be parallel if the angle between the vectors is 0° or 180° i.e. cosθ=-1
Knowing these facts, let us compute the dot product:
[tex]u\cdot v=(-4*28)+(7*-49)=(-112)+(-343)=-455[/tex]
Since the dot product of the two vectors is not 0, then the vectors are not orthogonal, so we can eliminate choices A and B
To check if the vectors are parallel, find the angle between them:
[tex]\displaystyle\theta=cos^{-1}\biggr(\frac{u\cdot v}{||u||\:||v||}\biggr)\\\\\theta=cos^{-1}\biggr(\frac{-455}{\sqrt{(-4)^2+(7)^2}\sqrt{(28)^2+(-49)^2}}\biggr)\\\\\theta=cos^{-1}\biggr(\frac{-455}{\sqrt{16+49}\sqrt{784+2401}}\biggr)\\\\\theta=cos^{-1}\biggr(\frac{-455}{\sqrt{65}\sqrt{3185}}\biggr)\\\\\theta=cos^{-1}\biggr(\frac{-455}{\sqrt{207025}}\biggr)\\\\\theta=cos^{-1}\biggr(\frac{-455}{455}\biggr)\\\\\theta=cos^{-1}(-1)\\\\\theta=180^\circ[/tex]
So, since the angle between the two vectors is 180°, this implies that cosθ=-1, and the two vectors must be parallel.
Thus, D is the correct answer
