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Math P1

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ny:
but the questions are just like that.
most of us didnt answer well on that questions.

nid404:

--- Quote from: ny on May 11, 2010, 02:53:34 am ---hello.i have this vector question for P1.
actually it was my mock exam question.

the question is:
the points A and B are such that the unit vector in the direction AB(from A to B) is 1/3i + pj +2/3k , where p is a negative constant.

i) find the value of p

then, the position vectors of A and B, relative to an origin O, are 9i +2j +qk and 12i -4j -5k respectively.

ii) find the value of q

thats all.thank you soo much.please reply asap..

--- End quote ---

Then I would wish to make a change here 1/3i + pj +2/3k  you mean 1/3 ( i+pj+ 2/3k) 
by which you mean 3 is the modulus of the vector

then to your first part

i) |AB|=

   |AB|=3
so =3
         
You should get p when you solve this

but i should know what im assuming is right  :-\
               

ny:
okay2.
its a bit different from the one in the marking scheme.

i) (1/3)2 + p2 + (2/3)2 = 1

p2= 4/9
p= -(2/3)

immortal:

--- Quote from: ny on May 11, 2010, 02:53:34 am ---hello.i have this vector question for P1.
actually it was my mock exam question.

the question is:
the points A and B are such that the unit vector in the direction AB(from A to B) is 1/3i + pj +2/3k , where p is a negative constant.

i) find the value of p

then, the position vectors of A and B, relative to an origin O, are 9i +2j +qk and 12i -4j -5k respectively.

ii) find the value of q

thats all.thank you soo much.please reply asap..

--- End quote ---

I think u missed out something..
anyway da first part cn b done using nid404's method

ii>da ratio of i:k  =1:2
   AB~(12-9)i+(-4-2)j+(-5-q)k
          3i-6j+(-5-q)k
  
Tere4     using   1:2
             -5-q=6
               q=-11
Now its also possible 2 find p
As da ratio is 3:6  =1:2
p=-2/3 (as p is a negative constant)

immortal:

--- Quote from: ny on May 11, 2010, 08:19:41 am ---okay2.
its a bit different from the one in the marking scheme.

i) (1/3)2 + p2 + (2/3)2 = 1

p2= 4/9
p= -(2/3)

--- End quote ---
ya ,i got got da same ans using  da method,but wasnt sure.so didint wont confuse u>

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