Question

Find a • b.

a = 5i + 7j, b = -4i + 3j

Answer 1

what?

Answer 2

You want the "dot product" of two given vectors?

There are 2 or 3 formulas used for "dot product."

Which do you propose to use?

Note that a dot product results in a scalar, whereas a cross product results in another vector.

Answer 3

-20, 21?

Answer 4

Where is the formula that you plan to use?

Answer 5

-20, 21 by itself is not the dot product of those 2 vectors. Again: a dot product returns a scalar, and there is no comma " .< " in the answer.

Answer 6

Looking for and sharing the appropriate dot product formula might clear things up for you as well as show the rest of us how you obtained your proposed answer.

Answer 7

haa, sorry, i am half sleeping, it is a determanate

Answer 8

i know it is placed like <-20,21>

Answer 9

wait so I am wrong?

Answer 10

Then, Abbs...., you are saying that the result of the dot product of 2 vectors is another vector? Not so.

Answer 11

Then i am confused

Answer 12

Abbs ... for the third time, I'm asking you to look for and then share the formula for "dot product."

Answer 13

i said all that crap, i was doing +

Answer 14

Dan, where would you look for the formulas for the dot product and the cross product of two vectors? Please share that info with Abbs.

Answer 15

the determinant of a 2x2 matrix for those 2 vectors

Answer 16

Why the negative sign. I wanna see your formula, Dan.

Answer 17

Abbs: I hope you're busy right now looking for the formula for the dot product.

Answer 18

-20 - 21

Answer 19

Look: vector a is given by <5,7>. Vector b is given by <-4,-3>.

We want the dot product. We do not want the determinant.

Answer 20

Abbs...have you found that formula yet?

Answer 21

I'm super confused now idk

Answer 22

I'm sorry Abbs, but at your level, able to study and learn dot and cross products, you MUST know where and how to find formulas for both. Why are you resisting doing that?

Answer 23

hmm you seem to be very rude, I will find someone elses help :)

Answer 24

dot product of 2 vectors , is the sum of the component products

<a,b>*<c , d> = ac + bd

Answer 25

you get some number,

Answer 26

Correct, Dan, and the resulting "number" is a SCALAR, not a vector.

Answer 27

the cross product is for vectors in 3 space

Answer 28

Dan, thank you so much for looking up this formula. Where did you find it?

Answer 29

i just remembered, hah sorry i am quitting now, sleeping

Answer 30

Actually, the cross product is of TWO vectors, with the resultant being a vector perpendicular to the first two. Good night, Dan.

Answer 31

cross product of 2 vectors will be another vector perpendicular to both of the cross terms

Answer 32

So, yes, we'll have 3 vectors in a 3-space.
Say this instead: the cross product of two vectors is a third vector perpendicular to the first two.

Answer 33

yeah the 3x3 determinant of , the unit vector and the 2 product vectors

Answer 34

too bad you're leaving. It'd be great if y ou could demonstrate that.
Abbs: do you want to continue or have you excused yourself from this discussion?

Answer 35

yeah normal to the plane of V1 and V2..

been a few years since actually doing the Calc 3 things with planes and lines and products

Answer 36

glad you remember as much as you do!

Unfortunately, Abbs has left this discussion, so I'm closing it. Thanks for your contributions!

Answer 37

ok