Question

If vector a=-8(vector b) and vector c=7(vector b) and what is angle between a and c ??

Answer 1

cos(t) = a*c/|a||c|

Answer 2

b*b = |b|^2

Answer 3

<-8xb, -8yb>
< 7xb, 7yb>
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-xb + -yb = -1<b>

Answer 4

thats messed up lol

Answer 5

yeah.. i didnt really understand that..

Answer 6

what do u mean in ur 3rd reply..??

Answer 7

a*c = -8<xb,yb> * 7<xb,yb>

Answer 8

-56x^2b + -56 y^b is the only values we can get from it right?

Answer 9

-56|b|^2 is the top value

Answer 10

the bottom is -8|b| * 7|b| = -56|b|^2

cos(t) = 1

Answer 11

t = 90 begrees right?

Answer 12

so hard to type in the dark lol

Answer 13

or it might just be 180 degrees; since a and c are scalars of b and they are facing inopposite directions.

Answer 14

I worked it similarly. I don't know if we got same place.
\[-8b.-7b =\left| a \right|\left| c \right|\cos \theta\] \[-8b.-7b =8b7b \cos \theta\] \[-1=\cos \theta\] \[\cos^{-1} -1=\theta\] \[\theta = 3.14 (radians)\]

Answer 15

I didn't dot the left hand side. May be that is a mistake that needs to be cleaned up. I should go to sleep now.