Question

find the measure of the angle ABC.

given:

A(3,0,0)
B(0,1,0)
C(1,2,3)

Answer 1

Perimeter?

Answer 2

no have to find the angle :)

Answer 3

hmm....let me see a formula..I've 4gotten it :(

Answer 4

cosθ=(x1x2+y1y2+z1z2)/|u||v|

Answer 5

thats what i used but it could be the wrong formula

Answer 6

(a1a2a3+b1b2b3)
the angle between 2 lines is cosA =------------------------------------
sqr(a1^2+b1^2+c1^2)*sqr(a2^2+b2^2+c2^2)

k1k2+1
Or cosA=---------------------------
sqr(k1^2+1*sqr(k2^2+1)

Answer 7

too messy

Answer 8

yes i used the same formula i dont know why my answer came out wrong

Answer 9

is the angle between vector AB and vector AC correct

Answer 10

i thought u might have to find the eq of the lines and then use the coefficients or slopes...

Answer 11

AB(-3,1,0) and AC(-2,2,3)

Answer 12

i dont think so. But i could be wrong

Answer 13

Or i can be wrong...

Answer 14

lol

Answer 15

omg this is killing me:)

Answer 16

I don't have the idea how to do it...:S:S ...Sorry..:(:(
Survive till some1 else helps u though :P:P

Answer 17

lol ill try

Answer 18

^_^ lol

Answer 19

this is what i got

Answer 20

and have you opened it?

Answer 21

yep just a quick question. when you find the vector AB shouldnt it be the vector b-a?

Answer 22

you know i was never sure about that
lol
you are probably right
i never had a class on this, but i have looked at it

Answer 23

AB and BA have different direction so they are different vectors right?

Answer 24

thats correct

Answer 25

i know we want to find angle B so I know I'm suppose to use CB/BC and AB/BA
but i'm not sure what to use
maybe I think i;m suppose to use AB and BC

Answer 26

yes i was thinking the same the thing is when i use AB and AC my answer is wrong lol

Answer 27

AB=<0-3,1-0,0-0>
BC=<1-0,2-1,3-0>

Answer 28

AB dot BC=-3(1)+1(1)+0(3)=-3+1=-2
mag{AB}=sqrt{9+1}=sqrt{10}
mag{BC}=sqrt{1+1+9}=sqrt{11}

Answer 29

\[\cos^{-1}(\frac{-2}{\sqrt{110}})\]

Answer 30

what do you think of that?

Answer 31

the answer is \[\approx 79.01 degrees\]

Answer 32

so your working out before was closer the answer

Answer 33

omg the first one i had was right

Answer 34

lol sorry

Answer 35

so its BC and BA

Answer 36

so yes
i labeled them wrong
that is so weird how i didn't bother with the directions and i wounded up doing the right way with wrong labels

Answer 37

lol

Answer 38

thanks heaps :)

Answer 39

thanks for teaching me alittle bit about vectors

Answer 40

Congratz guys :)

Answer 41

by the way and you called me a guy earlier
i am not
lol

Answer 42

using BC and BA make sense since we listed the angle we looking for first
that angle being B