Question

How to find the angle between vectors?

Answer 1

#17.

A is 42, right? What formula would I use to find b?
And what is the difference between c and d? o.O
Thanks!

Answer 2

Dot product is the sum of the products, component wise, yes?
So \(\large\rm \vec v_1\cdot\vec v_2=(-6)(-3)+4(6)\)

Answer 3

For B use the formula
(v1) . (v2) = |v1||v2|Cos angle

Answer 4

Zep, so I was right for number one? 42?
Faiq - thanks! I'll let you know what I get...

Answer 5

No, I'm getting 6 I think.
Part B doesn't make any sense.
I assume they want the angle between v1 and v2.
You can't find an angle between magnitudes, that doesn't make sense.

Answer 6

Hmmm
lol

Answer 7

(−6)(−3)+4(6)
18 + 24
= 42
no?

Answer 8

\(\color{#0cbb34}{\text{Originally Posted by}}\) @zepdrix
No, I'm getting 6 I think.
Part B doesn't make any sense.
I assume they want the angle between v1 and v2.
You can't find an angle between magnitudes, that doesn't make sense.
\(\color{#0cbb34}{\text{End of Quote}}\)
You can use the formula I mentioned.

Answer 9

Faiq, like this?
\[42 = \sqrt{52} * \sqrt{25}cosx\]

Answer 10

And then solve for x?

Answer 11

Oh yes you're right :)
I missed the other minus sign, derp.

Answer 12

I am getting root 52 and root 45

Answer 13

Right, you're right! Lemme redo it.. otherwise was it good tho?

Answer 14

Zep, you derp :)

Answer 15

Zep your math is bad and you should feel bad! https://youtu.be/jG2KMkQLZmI

Answer 16

Agent, your sense of humor...
it's funny because you're so serious most of the time :D

Answer 17

Faiq, is the angle 29.74 degrees?

Answer 18

Correct

Answer 19

For c
\[\large \rm proj_ab=\frac{a.b}{|a|}\]
For d
\[\large \rm proj_ab=\frac{a.b}{|a|^2}a\]

Answer 20

Thank you!!!
For c, would it be 42/sqrt52 ?

Answer 21

What unit would that be?

Answer 22

Correct and no units

Answer 23

\[\frac{ 45 }{ 52 }(-6, 4)\]

Answer 24

For d?

Answer 25

correct

Answer 26

Thank you so much :)

Answer 27

The pleasure wasn't mine. (JK)

Answer 28

Hey Faiq? I have a question...
For C, I just tried plugging it into a calculator (to check) and the answer is different than the one I have
https://www.symbolab.com/solver/vector-scalar-projection-calculator/scalar%20projection%20%5Cbegin%7Bpmatrix%7D-3%266%5Cend%7Bpmatrix%7D%2C%20%5Cbegin%7Bpmatrix%7D-6%264%5Cend%7Bpmatrix%7D
What do you think?

Answer 29

https://en.wikipedia.org/wiki/Scalar_projection
They are using the wrong formula

Answer 30

Okay, just making sure.. :)
Thank you ! <3

Answer 31

Whoa http://1.bp.blogspot.com/-WoUUXMMOMbs/U1kVUfMUXXI/AAAAAAAAAc0/E38YCtP95Vg/s1600/1.png

Answer 32

WHOA http://www.tbwnz.com/image45/vyiuuetsfyhiguxovvye.jpg