Mathematics: Post your doubts here!

[Rutzaba]

I´ll post this once, once, again...

I´ve got a question and would appreciate some help.

For Q9(i), if you are trying to find the normal to the plane using vector product, why if you do AC x AB or CA x BA you get a wrong answer, but if you use any other two vectors, you get the correct normal to the plane? The only difference for the normal to the plane I get using AC x AB or CA x BA is a minus sign for the k coordinate, instead of a positive one (just asking this in the case someone knows an explanation for it).

I would also like if someone could clarify me how to use vector product correctly, ie. what requisites should the vectors you are going to use for vector product have?

ALSO, how do you do Q9(ii).

Thank you in advance.

formula be like
n1.n2=|n1||n2|cos theta
to find norm vector of abc
ab cross cb
oa-ob== 1,-2,0
oc-ob= 0,-1,2
cross of these...
-4,-2,-1 let this be n1

then to plane oab
oa-ba
oa = 2,0,0
ba= oa-ob=1,-2,0
cross of these will give
0,0,-4 this is n2
put in the form...
(0,0,-4).(-4,-2,-1)= root 16 *root 21 cos theta
4=4 root 21 into cos theta
1/root 21=cos theta
theta = cos inverse of 1/root 21
theta=77.4

 

[Magnanimous!!!]

Guys.. in october november 2004 how do u solve question number 16?
Can someone plzz help me....

 

[Rutzaba]

Have you read what I wrote? I dont get why i get a WRONG answer using AC x AB or CA x BA, but if you use any other two vectors, you get the correct normal to the plane.

thats wat my sir told me if you are uusing two combinations make sure that both have the same last letter...
such as CB cross AB or BA cross CA and make that letter the letter in the middle such as in ABC make the repeated letter to be B

 

[robinhoodmustafa]

thats wat my sir told me if you are uusing two combinations make sure that both have the same last letter...
such as CB cross AB or BA cross CA and make that letter the letter in the middle such as in ABC make the repeated letter to be B

baji idhar please.
Q8 part 1 .
http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_s13_qp_11.pdf
app aik bar explain kardey

 

[Rutzaba]

Guys.. in october november 2004 how do u solve question number 16?
Can someone plzz help me....

wat world do u live in ? there are only 11 questions in the ppr

 

[Rutzaba]

baji idhar please.
Q8 part 1 .
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s13_qp_11.pdf
app aik bar explain kardey

ye bataya to tha robin... -_-
mere kal 2 tests hain...

 

[Namehere]

thats wat my sir told me if you are uusing two combinations make sure that both have the same last letter...
such as CB cross AB or BA cross CA and make that letter the letter in the middle such as in ABC make the repeated letter to be B

well, i did it with CA x BA (same as what u said, BA x CA), and I get it wrong. I didn´t understand what u said about the letter in the middle, could you clarify please?

Also, if anyone can answer me, in the marking scheme it said for doing vector products, choose any vector parallel to the plane, so my question is, are any vectors in the plane parallel to the plane?

Thank you in advance!

 

[Rutzaba]

well, i did it with CA x BA (same as what u said, BA x CA), and I get it wrong. I didn´t understand what u said about the letter in the middle, could you clarify please?

Also, if anyone can answer me, in the marking scheme it said for doing vector products, choose any vector parallel to the plane, so my question is, are any vectors in the plane parallel to the plane?

Thank you in advance!

like in plane abc u use ab cross cb
if it is dac then da cross ca

 

[Rutzaba]

well, i did it with CA x BA (same as what u said, BA x CA), and I get it wrong. I didn´t understand what u said about the letter in the middle, could you clarify please?

Also, if anyone can answer me, in the marking scheme it said for doing vector products, choose any vector parallel to the plane, so my question is, are any vectors in the plane parallel to the plane?

Thank you in advance!

wch question dear?

 

[Rutzaba]

baji idhar please.
Q8 part 1 .
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s13_qp_11.pdf
app aik bar explain kardey

2x²-12x+13
divide frst two terms by 2 to get coeef of x²as 1
2(x²-6x) +13
then further divide the 6x by two (to satisfy 2ab part in a²-2ab +b²)
2(x²-6x +3²-3²) +13
2(x²-6x +9) -18+13
2(x-3)² -5

 

[Suchal Riaz]

Have you read what I wrote? I dont get why i get a WRONG answer using AC x AB or CA x BA, but if you use any other two vectors, you get the correct normal to the plane.

A.B and B.A are same
AXB and BXA are different.

 

[Namehere]

wch question dear?

Q9(i)

 

[Namehere]

A.B and B.A are same
AXB and BXA are different.

Ok, so whats your way when dealing with vector products?

 

[Suchal Riaz]

Ok, so whats your way when dealing with vector products?

I haven't done vectors of P3. i was just confirming that A x B is not same as B x A.

 

[***amd***]

I haven't done vectors of P3. i was just confirming that A x B is not same as B x A.

I guess, no. coz when we write them in matrix form then A * B is not always equal to B * A

 

[Suchal Riaz]

I guess, no. coz when we write them in matrix form then A * B is not always equal to B * A

i said the same thing -_- that they are different. i was not asking i was confirming them .

 

[***amd***]

i said the same thing -_- that they are different. i was not asking i was confirming them .

ok then, i assured you

 

[Rutzaba]

Namehere

formula be like
n1.n2=|n1||n2|cos theta
to find norm vector of abc
ba cross bc
oa-ob== 1,-2,0
oc-ob= 0,-1,2
cross of these...
-4,-2,-1 let this be n1

then to plane oab
oa-ba
oa = 2,0,0
ba= oa-ob=1,-2,0
cross of these will give
0,0,-4 this is n2
put in the form...
(0,0,-4).(-4,-2,-1)= root 16 *root 21 cos theta
4=4 root 21 into cos theta
1/root 21=cos theta
theta = cos inverse of 1/root 21
theta=77.4

 

[Namehere]

Namehere

Thank you!

 

[Magnanimous!!!]

Dose anyone know how to use the matrices function on the calculator?