Question

If v1 = (-2,5) and v2 = (4, -3), then the angle between the two vectors is _____°

Round your answer to two decimal places.

Here is what I did:

I multiplied vs and v2 and got -23.

then |v1||v2| = √((-2)^2 + 5^2)*√(4^2 + (-3)^2) = √(29)*√(25) = √(725)

-23/√(725) = -.85 radians = -48.7°

Did I do it correctly?

Answer 1

do you know how to dot two vectors?

Answer 2

theta = cos^-1((v1(dot)v2)/(v1*v2))

Answer 3

the dot product is 4, right?

Answer 4

-2*4+5*-3

Answer 5

oh right, accidentally added

Answer 6

-23

Answer 7

theta = cos^-1((v1(dot)v2)/(|v1|*|v2|))

Answer 8

now do you know how to find the magnitude of the two vectors?

Answer 9

no

Answer 10

first one is sqrt((-2)^2+5^2)

Answer 11

sqrt 29

Answer 12

do the same for the second one

Answer 13

5

Answer 14

ok now cos^-1(-23/(5*sqrt(29)))

Answer 15

148.4°

Answer 16

looks right to me:)

Answer 17

Great, Thanks!

Answer 18

http://www.wolframalpha.com/input/?i=find+the+angle+between+%3C-2%2C5%3E+and+%3C4%2C-3%3E

Answer 19

np

Answer 20

remember

a(dot)b = |a|*|b|*cos(theta) where theta is the angle between them
and |a| = sqrt(a_1^2+a_2^2+.......+a_n^2)

Answer 21

so whats the answer?