Question

Calc help please!

Answer 1

Which one's are we stuck on? All of them? :)

Answer 2

Yes please :( I'm just learning this

Answer 3

I don't remember vectors very well...
But let's see what we can figure out.
\[\Large\rm \vec a=<\quad2,-1,\quad3>\]\[\Large\rm \vec b=<\quad4,\quad1,-5>\]\[\Large\rm \vec c=<-2,\quad 6,\quad 1>\]

Answer 4

Alright so i'll start by subing in the values

Answer 5

\[\Large\rm (\vec a+\vec b)\cdot3\vec c\]
Understand how to do the addition portion?

Answer 6

um would it be (2,-1,3+4,1,-5).3(-2,6,1)

Answer 7

would it be (6,0,-2).3(-2,6,1) ?

Answer 8

\(\Large\rm \vec a+\vec b=<\quad6,\quad0,-2>\)
Mmm ok good, the addition looks correct.
The way you wrote it the first time had me worried.

We need to distribute the 3 to the vector c before we can dot product.

Answer 9

so then (6,0,-2).(-6,18,3)

Answer 10

then would it be (-36,0,-6) ? :l

Answer 11

Ok close.
You did the multiplication correctly.
But remember for dot product we add all of these products together.

Answer 12

When doing dot product, we don't end up with a vector.
We end up with a number, a scalar value.

Answer 13

\[\Large\rm \left(\vec{a}+\vec{b}\right)\cdot3\vec c=-36+0-6\]

Answer 14

so -42 ?

Answer 15

Good :)

Answer 16

okay that was petty easy :) thanks !

Answer 17

\[\Large\rm \left(\vec{a}\times\vec{b}\right)\cdot\vec{c}\]

Answer 18

would I do foil for the multiplication or the same way as I did before ?

Answer 19

(2,-1,3)(4,1,-5).(-2,6,1)

Answer 20

(8,0,15).(-2,6,1) or no ?

Answer 21

No, cross product is a little trickier than that.
Mmmmm I'm trying to think of a good way to explain this...

Answer 22

oh I think my teacher taught me this I'll try to remember

Answer 23

cross product will be the determinant of this matrix.