Author Topic: Need help in C4 vectors  (Read 1505 times)

Offline T.Q

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Need help in C4 vectors
« on: April 20, 2010, 10:56:36 am »
The line l1 has vector equation

r = 8i + 12j + 14k + t(i + j – k),

where t is a parameter.

The point A has coordinates (4, 8, a), where a is a constant. The point B has coordinates
(b, 13, 13), where b is a constant. Points A and B lie on the line l1.

(a) Find the values of a and b.
(3)

Given that the point O is the origin, and that the point P lies on l1 such that OP is
perpendicular to l1,

(b) find the coordinates of P.
(5)


i need help in part B  with explanation plz
No Matter What Happens In Life , Just Don't Lose Hope :)

Amr Fouad

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Re: Need help in C4 vectors
« Reply #1 on: April 20, 2010, 10:58:44 am »
Sorry Cant help ya :(

I am still doing my A-Ls this year..

Maybe Astar or nid can  :(

Offline T.Q

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Re: Need help in C4 vectors
« Reply #2 on: April 20, 2010, 11:01:20 am »
Sorry Cant help ya :(

I am still doing my A-Ls this year..

Maybe Astar or nid can  :(

no problem

i will wait for them :)
No Matter What Happens In Life , Just Don't Lose Hope :)

nid404

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Re: Need help in C4 vectors
« Reply #3 on: April 20, 2010, 11:03:29 am »
Can u post your answers for the first part...

Offline T.Q

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Re: Need help in C4 vectors
« Reply #4 on: April 20, 2010, 11:05:48 am »
Can u post your answers for the first part...


a=18

b=9
No Matter What Happens In Life , Just Don't Lose Hope :)

nid404

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Re: Need help in C4 vectors
« Reply #5 on: April 20, 2010, 11:13:18 am »
I need to know how u got it....
I can't help otherwise...if i get this i can help using my iit books
Cuz evn im doing AS

Amr Fouad

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Re: Need help in C4 vectors
« Reply #6 on: April 20, 2010, 11:16:50 am »
I need to know how u got it....
I can't help otherwise...if i get this i can help using my iit books
Cuz evn im doing AS


if ur doing AS, then i guess u can do nth in this q.  :-\

nid404

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Re: Need help in C4 vectors
« Reply #7 on: April 20, 2010, 11:17:49 am »
if ur doing AS, then i guess u can do nth in this q.  :-\

I'm doing iit as well...that's engineering entrance stuff...
so if he can tell how he derived the ans to the first part...i maybe able to do some good..hopefully

Offline T.Q

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Re: Need help in C4 vectors
« Reply #8 on: April 20, 2010, 11:18:59 am »
I need to know how u got it....
I can't help otherwise...if i get this i can help using my iit books
Cuz evn im doing AS


to find a

4=8+t
t= -4

a=14-t
a=18


to find b

13=12+t
t= 1

b=8+t
b=9
No Matter What Happens In Life , Just Don't Lose Hope :)

Offline T.Q

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Re: Need help in C4 vectors
« Reply #9 on: April 20, 2010, 11:24:12 am »
I'm doing iit as well...that's engineering entrance stuff...
so if he can tell how he derived the ans to the first part...i maybe able to do some good..hopefully

its okay nid

i will wait for astar
No Matter What Happens In Life , Just Don't Lose Hope :)

Offline astarmathsandphysics

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Re: Need help in C4 vectors
« Reply #10 on: April 20, 2010, 11:28:14 am »
Here

Offline astarmathsandphysics

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Re: Need help in C4 vectors
« Reply #11 on: April 20, 2010, 11:38:46 am »
The line l1 has vector equation

r = 8i + 12j + 14k + t(i + j – k),

where t is a parameter.

The point A has coordinates (4, 8, a), where a is a constant. The point B has coordinates
(b, 13, 13), where b is a constant. Points A and B lie on the line l1.

(a) Find the values of a and b.
(3)

Given that the point O is the origin, and that the point P lies on l1 such that OP is
perpendicular to l1,

(b) find the coordinates of P.
(5)


i need help in part B  with explanation plz
a)to find a  8i + 12j + 14k + t(i + j – k) =4i+8j+ak
equate the i's to get 8+t=4 so t=-4
equate the j's to get 12+t=8 so again t=-4
equate the k's to get 14-t=14--4=18=a
To find b 8i + 12j + 14k + t(i + j – k) =bi+13j+13k
equate the i's to get 8+t=b (1)
equate the j's to get 12+t=13 so t=1
equate the k's to get14-1=13 so t=1
then from (1) b=9
The tangent vector of the line is (1,1,-1)=v
OP.v=0 since they are perpendicular
OP=8i + 12j + 14k + t(i + j – k)=(8+t)i+(12+t)j+(14-1)k
OP.v=8+t+12+t-(14-t)=6+3t=0 t=-2 then P=8i + 12j + 14k -2(i + j – k)=6i+10j+16k

Offline T.Q

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Re: Need help in C4 vectors
« Reply #12 on: April 20, 2010, 11:45:44 am »
The line l1 has vector equation

r = 8i + 12j + 14k + t(i + j – k),

where t is a parameter.

The point A has coordinates (4, 8, a), where a is a constant. The point B has coordinates
(b, 13, 13), where b is a constant. Points A and B lie on the line l1.

(a) Find the values of a and b.
(3)

Given that the point O is the origin, and that the point P lies on l1 such that OP is
perpendicular to l1,

(b) find the coordinates of P.
(5)


i need help in part B  with explanation plz
a)to find a  8i + 12j + 14k + t(i + j – k) =4i+8j+ak
equate the i's to get 8+t=4 so t=-4
equate the j's to get 12+t=8 so again t=-4
equate the k's to get 14-t=14--4=18=a
To find b 8i + 12j + 14k + t(i + j – k) =bi+13j+13k
equate the i's to get 8+t=b (1)
equate the j's to get 12+t=13 so t=1
equate the k's to get14-1=13 so t=1
then from (1) b=9
The tangent vector of the line is (1,1,-1)=v
OP.v=0 since they are perpendicular
OP=8i + 12j + 14k + t(i + j – k)=(8+t)i+(12+t)j+(14-1)k
OP.v=8+t+12+t-(14-t)=6+3t=0 t=-2 then P=8i + 12j + 14k -2(i + j – k)=6i+10j+16k


thanx astar  :)

+rep
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