# Dot prodcuts

1. Sep 15, 2007

ii think i did this correct ( i hate projections)

1. The problem statement, all variables and given/known data

find the scalar and vector projections of b onto a

2. Relevant equations

a= (-1, -2 2) b=( 3,3,4)

scalr (a dot b)\|a|
vector (a dot b)\|a| * a/|a|

3. The attempt at a solution

(a dot b)\|a| =(1 =6 +8)/3 =1/3=scalar
1/3* (a/|a|)= 1/3 *(1/3)*a =-1/9, -2/9, 2/9

2. Sep 16, 2007

i meant to put (-3 -6 +8)/3 =1/3

3. Sep 16, 2007

### dynamicsolo

(He returns after catching his miscopying of a value...) Check your arithmetic here: there is an error in your dot product calculation. Your method looks all right, so the rest should fall into line from there.

4. Sep 16, 2007

a dot b

a = (-1, -2 ,2) b=(3,3,4)

-1(3) +(-2)(3) +2(8)= -3 +-6 +8..ooooooh -1 hahaa

is that the erorr you meant

5. Sep 16, 2007

### dynamicsolo

I believe that should do it. Everything else looked right -- basically, your vector projection components will just flip sign. Does that get you the right result?

6. Sep 16, 2007