Author Topic: [CIE] All Pure Mathematics (P1, P2 and P3) doubts here !  (Read 79954 times)

elemis

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #150 on: March 29, 2011, 07:44:07 am »
Thanks man,sorry for the trouble but i dont get Q6 part 1 in the same paper :(

Hold on.

elemis

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #151 on: March 29, 2011, 07:49:22 am »
If you have a complex number such as :

a + bi

Then, the modulus is : \sqrt{a^2+b^2}

For finding the argument of a complex no. :

Read your P3 textbook. There's an explanation in there.


Offline HUSH1994

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #152 on: March 29, 2011, 08:28:59 am »
i already got that before,thanks man,but i have a prob with Q9 part b part 2

elemis

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #153 on: March 29, 2011, 08:29:24 am »
i already got that before,thanks man,but i have a prob with Q9 part b part 2

Okay...

elemis

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #154 on: March 29, 2011, 08:34:13 am »
Use the sum of an arithmetic progression formula and substitute :

\frac{m}{2}[2*100+(m-1)(-5)]=\frac{m+1}{2}[2*100+(m+1-1)(-5)]

You already know what the first term and the common difference is from (b)(i)

Offline HUSH1994

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #155 on: March 29, 2011, 08:54:39 am »
i dont know why i post the question,i get the way right after i post em :S

Offline iluvme

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #156 on: March 29, 2011, 06:51:09 pm »
PR = PA + 0.5 AE + 0.5 AB      Read the information given in the question CAREFULLY

PQ = PO + OD + 0.5 DG

Oh right, Thanks again Ari.

Feeling very very stupid.
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Offline Arthur Bon Zavi

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #157 on: March 29, 2011, 07:11:55 pm »
Oh right, Thanks again Ari.

Feeling very very stupid.

Any more doubts ? :P

Continuous efforts matter more than the outcome.
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Offline iluvme

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #158 on: March 29, 2011, 07:14:21 pm »
Any more doubts ? :P

Not right now. :P

Gotta start working again. :)
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Offline Arissa_04

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #159 on: April 04, 2011, 08:19:20 pm »
Hey guys, need help in a trig question.not sure which year it is is from.Here's how the question goes:

Using the expansion of cos(3x-x) and cos(3x+x) prove that:

                    1/2(cos2x - cos4x) = sin3x sinx

Its a 3 mark question so I'm pretty sure its not that complicated but I cant seem to get the answers.
Thanks in advance :)

Offline ashish

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #160 on: April 07, 2011, 05:07:32 pm »
Hey guys, need help in a trig question.not sure which year it is is from.Here's how the question goes:

Using the expansion of cos(3x-x) and cos(3x+x) prove that:

                    1/2(cos2x - cos4x) = sin3x sinx

Its a 3 mark question so I'm pretty sure its not that complicated but I cant seem to get the answers.
Thanks in advance :)

cos(3x-x)= cos2x
             =cos3x * cosx -- sin3xsinx
             =cos3xcosx + sin3xsinx

cos(3x+x)=cos4x
             =cos3xcosx-sin3xsinx

cos2x - cos4x = cos3xcosx + sin3xsinx -(cos3xcosx - sin3xsinx)
                    = 2sin3xsinx

half of it is sin3xsinx
                     

Offline Arissa_04

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #161 on: April 07, 2011, 08:34:59 pm »
Thanks so much Ashish.
That was  well explained..I cant believe I spent so much time on that question unnecessarily complicating things by expanding cos3x and so on..
Thank you :)

Offline thecandydoll

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #162 on: April 16, 2011, 11:36:02 am »
With respect to the origin O, the points A, B and C have position vectors given by
OA=i?k, OB=3i+2j?3k and OC=4i?3j+2k. The mid-point of AB is M. The point N lies on AC between A and C and is such that AN = 2NC.
(i) Find a vector equation of the line MN.   [4]
 (ii) It is given that MN intersects BC at the point P. Find the position vector of P.   [4]

I just dont get vectors sometimes,
any notes on this any notes on argand diagrams!
 thanks :D

elemis

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #163 on: April 16, 2011, 02:00:33 pm »
With respect to the origin O, the points A, B and C have position vectors given by
OA=i?k, OB=3i+2j?3k and OC=4i?3j+2k. The mid-point of AB is M. The point N lies on AC between A and C and is such that AN = 2NC.
(i) Find a vector equation of the line MN.   [4]
 (ii) It is given that MN intersects BC at the point P. Find the position vector of P.   [4]

I just dont get vectors sometimes,
any notes on this any notes on argand diagrams!
 thanks :D

Long time since I've done any vector work.

AB = -i+k+3i+2j-3k
     = 2i -2k +2j

AM = 0.5 AB
     = i-k+j

OM = OA + AM
     = 2i +j -2k

AC = 3i -3j +3k

AN = (2/3)AC
    =  2i -2j +2k

ON = OA + AN
     = 3i -2j +k

Vector equation = position vector of N +\lambda (position vector of N - position vector of M)

Part (b)

Find the vector equation of BC :

r = 3i+2j-3k + \mu(i -5j +5k)

Equate the equation from (a) with this new equation.

You will have three simultaneous equations.

Solve for lambda and mu. You should find lambda = 2 and mu =2

Re-insert back into one of the other equations and find the position vector of the cross over point.
« Last Edit: April 16, 2011, 02:08:33 pm by Ari Ben Canaan »

Offline HUSH1994

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Re: All Pure Mathematics DOUBTS HERE!!!
« Reply #164 on: April 16, 2011, 04:38:28 pm »
MJ 2004 Q10 part one,i was always wondering why do you have to change the sign of the least value,anyone knows that?