Maths & Physics Help

[blah4444]

can u pls explain qn no.11 in the may/june 2008 p2?
thanks

[astarmathsandphysics]

use the cosine rule a^2=b^2+c^2-2bc*cosA
21^2=x^2+92x)^2-x*2x*cos120
441=x^2+4x^2-4x^2*-1/2
441=5x^2+4x^2
441=9x^2
so x=sqrt(441/9)=7

[igvictim]

hey, thank you for the formulae sheet, it helped 

cheers

[qwerty]

hey..i have a doubt on factorising stuff

how do i know what method to use?

for example:

6ab - 9bx - 21by

i would easily transform into:

3b (2a - 3x - 7y)

but, for example:

k² + 9k + 8

what should be done?thanks!

[astarmathsandphysics]

First is correctt. In second look for 2 numbers that add to give 9 and times to give 8.
The answer is 1 and 8 so it factorises as (x+1)(x+8)

[unknown]

need help wth transformations
want d whole chap summarisd if possible
n ya need help in reflection where the mirror line is slanting

[astarmathsandphysics]

http://www.bbc.co.uk/schools/gcsebitesize/maths/shapes/transformationsrev1.shtml

It is summarized here.

[unknown]

hey thx a lot
bt ya need fr sheer too

[unknown]

the coordinates of the vertices of a square abcd after two transformation are as folllows
a(-2,2) b(2,2) c(2,-2) d(-2,-2)
a'(-2,6) b'(6,2) c'(2,-6) d'(-6,-2)
a"(-6,8) b"(-2,-4) c"(6,-8) d"(2,4)
a) find the matrix which maps abcd onto a'b'c'd'
b) find the matrix which maps a'b'c'd' onto a"b"c"d"
c) find the matrix which maps abcd onto a"b"c"d"
d) find the matrix which maps a"b"c"d" onto abcd (this shalll be d inverse of d ans c rite)

plzz give a detailed explanation of hw to get to d ans
the need is urgent
thx fr d help

[astarmathsandphysics]

the coordinates of the vertices of a square abcd after two transformation are as folllows
a(-2,2) b(2,2) c(2,-2) d(-2,-2)
a'(-2,6) b'(6,2) c'(2,-6) d'(-6,-2)
a"(-6,8) b"(-2,-4) c"(6,-8) d"(2,4)
a) find the matrix which maps abcd onto a'b'c'd'
b) find the matrix which maps a'b'c'd' onto a"b"c"d"
c) find the matrix which maps abcd onto a"b"c"d"
d) find the matrix which maps a"b"c"d" onto abcd (this shalll be d inverse of d ans c rite)

plzz give a detailed explanation of hw to get to d ans
the need is urgent
thx fr d help

2 2

[unknown]

i dont get it
wht is 2 2

[astarmathsandphysics]

i AM TRYING TO TYPE IN THE QUESTION. iT IS SO DIFFICUL

[astarmathsandphysics]

a)(a b)(-2)     (-2)
   (c d)(2)   =  (6)
multiply out to get -2a+2b=-2 and -2c+2d=2

Similarly with b to b' etc. Solove the simulateous equations in a and b c d to get the matrix (2 1)
                                                                                                                                                  (1 2)

b)Follow the procedure from a to get (0 -1)
                                                            (-1 1)

c)(0 -1)(2 1)
   (-1 1)(1 2 )


Multiply the matrices to get(-1 -2)
                                               (-1 1)

d) (1/3 -2/3)
    (1/3  -1/3)

It is dificult to give a detailed explanation with something like latex. We will have to get some notaion software.

[unknown]

hey thx fr d help bt srry to say i still dnt get it

[astarmathsandphysics]

I will see if I can scan and email you something. I have to set up my scanner for this computer. Will try and do it today.