Question

QUESTION IS DRIVING ME INSANE!! Help please:
Vector U = (4,-4,-3) and Vector V = (5,4,-1)

Find: (U dot V) U

I found that it's (28,-28,21) but I'm told that's wrong. What did I do wrong??

Answer 1

@Jack1

Answer 2

g'day man, howzit?

Answer 3

It's not good Jack1. This question is annoying me more than a scratched tongue.

Answer 4

you're like 99% there dude... negative x negative x negative = negative
so
(28,-28,-21) not 21...

Answer 5

all better now ;)

Answer 6

But 7(4,-4,-3) how 21?

Answer 7

gotta go dude, lectures bout to start

Answer 8

will post in class, sry

Answer 9

Fine, thanks and good luck.

Answer 10

Oh, for when you get back, I did have -21, it was a typo when I pute "21". So something is still amiss.

Answer 11

Please help :p

Answer 12

i think it is correct if you get like jack1 said

Answer 13

That would seem to be wrong though, I do my HW online. So it's both wrong.

Answer 14

And I did actually get it like him the first time around. Still wrong.

Answer 15

sorry then, looking forward for answer too.

Answer 16

:(

Answer 17

sorry minato:
your dot product (U.V) will give you a vector magnitude only, as you did above
so U.V = Ux * Vx + Uy + Vy + Uz + Vz
= 7 overall
then you are multiplying that by a vector: U, so the answer will be a vector

so U.V times U
= 7 times (4,-4,-3)
= (7 * 4) , (7 * -4) , (7 * -3)
= 28, -28, -21

so final answer = (28, -28, -21) = a vector, rather than how the dot product was just a magnitude

Answer 18

just read that it was a typo... I believe the answer u and I got is correct man