## Babynini one year ago Projecting Vertex.

1. Babynini

2. Babynini

@acxbox22 :)

3. acxbox22

sorry i dont know this stuff :(

4. Babynini

@Nnesha

5. IrishBoy123

$$proj_{\vec{v}}\vec{u} = \frac{\vec{v} \bullet \vec{u}}{|\vec v|^2}\vec{v}$$ is the *vector* projection of $$\vec u$$ on $$\vec v$$. it's just a formula so calculate the various parts, eg $$\vec{v} \bullet \vec{u} = <11,3> \bullet <-6,-4>$$

6. IrishBoy123

$$| \vec v |^2 = \vec v \bullet \vec v$$

7. Babynini

so u * v = <-66,-12>

8. Babynini

yeah?

9. Babynini

simplified u*v=-78 v*v=52 is it right so far?

10. Babynini

@IrishBoy123

11. Babynini

@Loser66 :)

12. anonymous

can you help me plz

13. Babynini

Post your question on a new feed and i'll try :)

14. IrishBoy123

"u • v = <-66,-12>" nah u • v = <11,3).<-6,-4> = (11)(-6) + (3)(-4) = -66 - 12 = - 78

15. Babynini

yep yep that's what I got for that one :)

16. IrishBoy123

$$\vec u \bullet \vec v = <u_x,u_y> \bullet <v_x,v_y> = (u_x \times v_x) + (u_y \times v_y)$$

17. IrishBoy123

sorry, bandwith issues, i am clearly behind times. let me read the thread again

18. Babynini

It's all good :)

19. IrishBoy123

v.v = <-6,-4><-6,-4> = 36 + 16 = 52 seems we agree

20. IrishBoy123

what next?

21. Babynini

uh..not sure haha

22. Babynini

plug it into the formula?

23. IrishBoy123

yes <9,6>?

24. Babynini

so we have $\frac{ -78 }{ 52}v$

25. Babynini

woah where did you get<9,6> ?

26. IrishBoy123

v = <-6,-4> and, -78/52 = -3/2 and, -3/2 * <-6,-4> = <9,6> agree?

27. Babynini

ah I see, thanks :)

28. Babynini

so, is that the final answer then? o.0

29. Babynini

or ..is that just what $u _{1}$ equals?

30. IrishBoy123

that answers (a). for (b) you have to .....!!! do something v similar

31. Babynini

let's do it x)

32. Babynini

we would use (-75/52)v again, yeah?

33. IrishBoy123

you've already done $$\vec u_1$$ that's what you just calculated so you need to do the same on $$\vec u_2$$ so what is $$\vec u_2$$ ? it is orthogonal to $$\vec v$$ ...

34. Babynini

its $u - u _{1}$

35. Babynini

<2,-3>?

36. IrishBoy123

<-6,-4>•<x,y> = 0 -6x-4y = 0 try: <-6,-4>•<4,-6> or <-6,-4>•<-4,6> both work we can use either

37. Babynini

does what I did work? o.o

38. Babynini

I'm pretty sure that's what the prof did in class but ah well haha

39. IrishBoy123

let me actually do it

40. Babynini

k

41. IrishBoy123

<2,-3> Roger

42. Babynini

Yay! fantastic :)

43. Babynini

thanks for taking the time to calculate it all :)

44. Babynini

so we have $u _{1}=<9,6> u _{2}=<2,-3>$

45. Babynini

what goes into $proj _{v}u$?

46. Babynini

nevermind, they just wanted <9,-6> there too :) thanks!!