Major MATH HELP! D: ** Pic included!

- anonymous

Major MATH HELP! D: ** Pic included!

- katieb

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- anonymous

##### 1 Attachment

- anonymous

Help? :(

- anonymous

wat

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## More answers

- anonymous

I need some help with this problem

- anonymous

ok

- anonymous

wats ur answer

- anonymous

I dont have onne, I need help :| I attached a link of the problem

- anonymous

i did

- anonymous

hold on

- anonymous

thnx (:

- anonymous

Do you still need help?

- anonymous

Yes please (:

- anonymous

ya

- anonymous

Okay, Do you know how to even start working on this problem?

- anonymous

No :C

- anonymous

So are you working with vectors?

- anonymous

indeed I am!

- anonymous

Im just tottally lost on this problem

- anonymous

Ok, so have you done vector proofs before?

- anonymous

no neverO=

- anonymous

ok, so ob+ba=oa

- anonymous

0=(0,0) A=(x1,y1) B=(x2,y2)

- anonymous

Vector BA=A-B=(x1-x2, y1-y2)

- anonymous

okk

- anonymous

Good so far?

- anonymous

All what you have to do now is find vecotor OA and vecotr OB

- anonymous

O: oh really but is there like another pic you have to draw/

- anonymous

no

- anonymous

oh cool

- anonymous

|dw:1352869007184:dw|

- anonymous

so vector BA is equal to A-B
so when you subtract the points element-wise
you get x1-x2 and y1-y2

- anonymous

|dw:1352869116355:dw|

- anonymous

Oh right, now I find Oa Ob ?How can I do thta again?

- anonymous

|dw:1352869175679:dw|

- anonymous

now you do the same for vector ob

- anonymous

|dw:1352869297947:dw|

- anonymous

So OB is OB = O-B= <0-x2 , 0-y2 > ?

- anonymous

no, it would be = B-O =

- anonymous

So, now you need to subtract from . to prove that it equals

- anonymous

ohhh right!

- anonymous

##### 1 Attachment

- anonymous

look at the attachment, the circled ones.

- anonymous

How would you prove the?

- anonymous

*them?

- anonymous

They are equal.

- anonymous

so, by the subtraction of the vectors, you prove that = -

- anonymous

OH theyre equal!!
Its < x1-x2 , y1-y2 > !

- anonymous

pretty much.

- anonymous

Now to solve part 2, set point c equal to (x3, y3)

- anonymous

then I would solve for x3,y3 in terms of the other known quantities, x1,y1 and x2,y2 using the given ratio. the rest is just algebra.

- anonymous

So all what xOA is saying is to ditribute the x?

- anonymous

Ya

- anonymous

Oh okay yy

- anonymous

|dw:1352870110521:dw|

- anonymous

right?

- anonymous

yes.

- anonymous

Cool thanks ((:

- hartnn

- hartnn

- anonymous

you want me to isolare c from (C-B)/(A-C) =x/y
right?

- hartnn

yes,

- hartnn

u see, how i got, (C-B)/(A-C) =x/y
from given condition, / =x/y

- anonymous

Wait how would you do that because C is being subtracted

- hartnn

u mean how to isolate C ?
cross-multiply....

- anonymous

yea youd get y(c-b) = x(a-c) ...

- hartnn

try to isolate C from that...

- anonymous

so I distribute..first then

- anonymous

yc-cb = xa - xc

- hartnn

yes, distribute then bring all terms with 'c' together, then factor out c

- hartnn

its yc-yb on the left...

- anonymous

So C= xa-xc / (y-b)

- hartnn

there, u were not able to isolate C, notice, c is there on right side also

- hartnn

yc-yb = xa - xc
yc+xc = xa+yb
got this step ?

- hartnn

now can u isolate c ?

- anonymous

I thought ititd be yc-cb = xa - xc since u cross mult tho..

- anonymous

|dw:1352871594989:dw|

- hartnn

|dw:1352871643318:dw|

- anonymous

right x)

- hartnn

|dw:1352871704757:dw|

- anonymous

yesyes i did that xD

- hartnn

what does left side simplify to ?

- hartnn

knowing that its given that x+y=1

- anonymous

C= xa+yb / y+x

- hartnn

what is x+y= ?

- anonymous

Wait but does C equal to that O:

- hartnn

yes.

- anonymous

oh okay lol Um y+x = .. ?

- hartnn

its given to be =1
see the question

- anonymous

Oh cool so it would just be xa+yb

- hartnn

yes, c=xa+yb
now u know what to do next ?

- anonymous

PLug it to...

- hartnn

we know that C=(x3,y3)
and O=(0,0)
so can you find = ?

- anonymous

- hartnn

which is ?

- anonymous

x3,y3

- hartnn

so =C
so we can replace C by
right ?

- anonymous

ohhyeauhhh! ool!

- hartnn

in same way, we can replace A by ... ?
B by ... ?

- anonymous

A with x1,y1??

- hartnn

A with

- hartnn

- anonymous

yes..

- hartnn

so put all those in
c=xa+y
and see whether u get what needs to be proven..

- anonymous

|dw:1352872625517:dw|

- anonymous

Do u mean plug in the value sliket his

- hartnn

|dw:1352872688272:dw|

- anonymous

OH THATS what you ment I tots get that!

- hartnn

all steps clear ? any doubts ?

- anonymous

Wait and how did u kno that OC=c and OA =A and OB = B ?

- hartnn

C = (x3,y3)
=C-O = (x3,y3)-(0,0) = (x3-0,y3-0) = (x3,y3) = C
same for A and b

- hartnn

got it ?

- anonymous

yea thanks (: Do you think we can do another in like 10 min?? I I need to sleep asap since I need to wake up early tomorrow (x

- hartnn

same type ? ....actually even i need to go in few minutes...

- hartnn

lets me see the question atleast

- anonymous

OK but && Oh and alsoo how did you know that ( C- B)/(A-C) = x/y

- hartnn

it is given that BC /CA = x/y
now
BC=C-B
CA=A-C

- hartnn

remember for any vector XY, we can write it as Y-X

- anonymous

oh okay why is it flipped again?

- hartnn

flipped again ? means ?

- anonymous

Oh I mean like why isnt it like BC= B-c instead its C-B

- hartnn

its the conventional way of representation,
but if you take BC=B-C , you will get same exact final answer....

- hartnn

so its no difference, just a way of representation

- anonymous

Oh right k thnx!
lemme post the other problem I dont think we have enough tim :C

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