Question

Vectors A=(2,1,-4), B=(-3,0,1).
What is the angle (thetaAB) between A and B?
Can someone guide me or explain me how to solve this?

Answer 1

check out this page

http://www.mathsisfun.com/algebra/vectors-dot-product.html

the formula works for any type of vectors (in 2space, 3space, etc)

Answer 2

I did but I am still unsure how to do the problem above. I'm trying to figure it out.

Answer 3

what is the dot product of those two vectors?

Answer 4

to be honest I have 0 knowledge about vectors so I just started reading about it. I am not sure how to approach this one though.

Answer 5

your teacher never went over dot products at all?

Answer 6

Uhm well I just started physics on college and the professor started talking about it and I had never done that so I am completely lost on this subject.

Answer 7

did you look at the link I posted? Did that article make any sense at all?

Answer 8

it explains how to compute the dot product

basically you multiply the corresponding components, then add the products up

Answer 9

yes. I can solve for some but I still don't understand how to approach this by looking at the website.

Answer 10

I can do A*B = AxBx + AyBy + AzBz

Answer 11

what dot product did you get

Answer 12

but I am not sure how to approach this one

Answer 13

do I have to do something like this? A*B= (AxBx+AyBy+AzBz)cos(theta)?

Answer 14

close

Answer 15

on the left side, you should have |A|*|B|

the vertical bars tell us to find the length of each vector

Answer 16

actually wait hold on

Answer 17

the formula is actually

AxBx+AyBy+AzBz = |A|*|B|*cos(theta)

Answer 18

I see |A|*|B|*cos(theta)

Answer 19

yeah that's it

Answer 20

oh oh

Answer 21

|A|*|B|*cos(theta) is equal to the dot product

so the dot product and the angle between vectors are connected ideas