IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: sweetest angel on December 16, 2009, 05:54:15 am

Title: M1 doubt
Post by: sweetest angel on December 16, 2009, 05:54:15 am: june 2009 Q2 b) (attached)

this is the answer

R = (i - 3j) + (pi + 2pj) = (1 + p)i + (-3 + 2p)j
R is parallel to i ? (-3 + 2p) = 0
? p = 3/2

but i dnt get it. if R is parallel to i then the value of i=0 not j=0 ?
Title: Re: M1 doubt
Post by: T.Q on December 16, 2009, 03:22:35 pm: Quote from: sweetest angel on December 16, 2009, 05:54:15 am
june 2009 Q2 b) (attached)

this is the answer

R = (i - 3j) + (pi + 2pj) = (1 + p)i + (-3 + 2p)j
R is parallel to i ? (-3 + 2p) = 0
? p = 3/2

but i dnt get it. if R is parallel to i then the value of i=0 not j=0 ?

because i is a straight horizantal line so it will have a zero j
and because R is parallel to i ,then R will have the value of j equal to zero
thats why they took the j value equal to zero
Title: Re: M1 doubt
Post by: sweetest angel on December 16, 2009, 04:40:13 pm: ohhhhh...but we dnt knw if it passes through j or not so maybe it has a j value ???
Title: Re: M1 doubt
Post by: eightAs on December 25, 2009, 08:31:28 am: Quote from: sweetest angel on December 16, 2009, 04:40:13 pm
ohhhhh...but we dnt knw if it passes through j or not so maybe it has a j value ???
consider the whole set up on the $xy - plane$
consider an arbitrary vector and the unit vector $\vec{\imath}$
We assume both vectors are parallel.
Lets assume the arbitrary vector is $a \vec{\imath}$ + $b \vec{\jmath}$
Gradient of $\vec{\imath}$ = Gradient of the other vector
$\frac{\Delta y1}{\Delta x1} = \frac{\Delta y2}{\Delta x2}<br />\frac{0}{1} = \frac{b}{a}<br />\Rightarrow b = 0.<br />$
Thus if an arbitrary
vector and $\vec{\imath}$ are parallel, the co-effecient of j for the arbitrary vector has to equal 0.
Title: Re: M1 doubt
Post by: Ghost Of Highbury on December 30, 2009, 10:20:37 am: Quote from: sweetest angel on December 16, 2009, 04:40:13 pm
ohhhhh...but we dnt knw if it passes through j or not so maybe it has a j value ???

a vector (2D) has two components; i and j which define its direction.
It cannot "PASS" through j. its a component. It can pass through a point.