Question

Find the angle between the given vectors to the nearest tenth of a degree.

u = <8, 4>, v = <9, -9>

25.8°
35.8°
71.6°
81.6°

Answer 1

@wolf1728 can i get your help again?

Answer 2

This might help:

\[\vec u \cdot \vec v = |u||v| \cos \theta \]

Answer 3

i still dont get it

Answer 4

25.8°
35.8°
71.6°
81.6°

im supposed to get one of those

Answer 5

@TheSmartOne

Answer 6

@wio

Answer 7

Do you know the dot product?

Answer 8

not really, no

Answer 9

do you know how graph points?

Answer 10

no

Answer 11

@wio

Answer 12

You can't do this problem if you're not even able do graph vectors and guess the angle between them.

Answer 13

i tried it and i got 71.6 degrees

Answer 14

Okay, good

Answer 15

is that correct?

Answer 16

@wio

Answer 17

Let me see

Answer 18

ok @wio

Answer 19

Yes, it is correct

Answer 20

thanks

Answer 21

can you help me with this one? :

Evaluate the expression.

r = <9, -7, -1>, v = <2, 2, -2>, w = <-5, -2, 6>

v ⋅ w
@wio

Answer 22

i think its -26

Answer 23

That is right

Answer 24

last one:

Express the complex number in trigonometric form.

-2 + 2 sqrt(3) i

@wio

Answer 25

@Astrophysics

Answer 26

You already know complex numbers and you were having trouble with dot products?

Answer 27

UdotV=|U||V|cosa

Answer 28

Given \(z=x+iy\). We say \(z=re^{i\theta}\) where\[
r=\sqrt{x^2+y^2},\quad \theta = \arctan\left(\frac{y}{x}\right)
\]

Answer 29

a=arccos(u . v/(sqrt(u . u +v . v)))

Answer 30

this is what i got:
4(cos5pi/6 + i sin 5pi/6)

Answer 31

@dan815 @wio