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

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: halosh92 on April 07, 2010, 08:02:40 pm

Title: C2 DOUBT edexcel
Post by: halosh92 on April 07, 2010, 08:02:40 pm
A circle has the equation
x2 + y2 + 8x ? 4y + k = 0,
where k is a constant.
(a) Find the coordinates of the centre of the circle. (2)
Given that the x-axis is a tangent to the circle,
(b) find the value of k.

for part b...how to get the radius exactly?
Title: Re: C2 DOUBT edexcel
Post by: astarmathsandphysics on April 07, 2010, 11:41:59 pm
Because the exapression completes the square as  (y+2)^2 it is two from the x acxis to the centre so the radius of the circle is 2.
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 08, 2010, 07:36:53 am
can u explain how they got the angle here on wat basis?
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 08, 2010, 07:47:15 am
Sketch on the same diagram the graphs of y = sin 2x and y = tan
2
x for x
in the interval 0 ? x ? 360°.
(b) Hence state how many solutions exist to the equation
sin 2x = tan
2
x ,
for x in the interval 0 ? x ? 360° and give a reason for your answer.

I have the answers i just need an explanation for part a
thx
Title: Re: C2 DOUBT edexcel
Post by: astarmathsandphysics on April 08, 2010, 08:14:13 am
When I get up
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 08, 2010, 02:31:42 pm
could someone plz answer this question?? :-\ ??? ??? ???
Title: Re: C2 DOUBT edexcel
Post by: astarmathsandphysics on April 08, 2010, 07:19:37 pm
4 only include one or roots at 360, 0
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 09, 2010, 08:37:56 am
4 only include one or roots at 360, 0
i dont get why u chose such places to places the tan curve :S
Title: Re: C2 DOUBT edexcel
Post by: astarmathsandphysics on April 09, 2010, 12:22:02 pm
They asked for answers in the range 0-360
Title: Re: C2 DOUBT edexcel
Post by: vanibharutham on April 11, 2010, 06:40:21 pm
heres a way you can try

sin2x = tan2x
sin2x = sin2x / cos2x

sin2x cos2x = sin2x
sin2x cos2x - sin2x = 0
sin2x ( cos 2x - 1) = 0

sin 2x = 0 and cos 2x = 1

you come out with

x = 0, 90, 180, 270, 360
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 15, 2010, 11:11:02 am
a circle with centre O and radius 6 cm.
the  chord PQ divides the circle into a minor segemnt R1 of area A1
and  a major segment R2 of area A2. the chord PQ subtends an angle thita radians at O/
a) show that A1= 18 (thita- sin thita)
 given that A2= 3A1 and f(thita) = 2 thita - 2sin thita - pie
b) prove that f(thita)=0
c) evaluate f(2.3) and f(2.32) and deduce that 2.3<thita>2.32

how to do part b  and c
??
thxxx
Title: Re: C2 DOUBT edexcel
Post by: AS panic attack on April 16, 2010, 12:24:15 pm
can sme one solve this ques

the coefficient of x3 in the epansion of (2+x)(3-ax)4 is 30
find the values of the constant a.

please show step by step working
Thanks
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 16, 2010, 01:52:50 pm
can sme one solve this ques

the coefficient of x3 in the epansion of (2+x)(3-ax)4 is 30
find the values of the constant a.

please show step by step working
Thanks

a=1
a= sqrt 30
 is this the answer? if not post the correct answer please :)
Title: Re: C2 DOUBT edexcel
Post by: AS panic attack on April 16, 2010, 02:56:48 pm
A=1, (5+or-sqrt 105)/8

please show workings i need to know how to get da ans

Thanks
Title: Re: C2 DOUBT edexcel
Post by: Amr Fouad on April 16, 2010, 03:25:19 pm
give me 2 mins
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 16, 2010, 03:34:54 pm
A=1, (5+or-sqrt 105)/8

please show workings i need to know how to get da ans

Thanks

which paper is this?
Title: Re: C2 DOUBT edexcel
Post by: Amr Fouad on April 16, 2010, 03:41:49 pm
can sme one solve this ques

the coefficient of x3 in the epansion of (2+x)(3-ax)4 is 30
find the values of the constant a.

please show step by step working
Thanks

here u go..:)

@halosh, i answered ur angle question, check the post
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 16, 2010, 03:46:05 pm
here u go..:)

@halosh, i answered ur angle question, check the post

 thx AF  but i did the whole thing its correct except when i got stuck at solving the cubic function..how do i do that?
Title: Re: C2 DOUBT edexcel
Post by: past-papers on April 16, 2010, 03:51:46 pm
For C2, you will always get easy cubics and thus you will always be able to find one factor!!

In this case, you can see that if a=1 the equation is equal so you realise that (a-1) is a factor.

now divide by (a-1) and you will get a quadratic which you can easily factorise again...
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 16, 2010, 03:54:09 pm
For C2, you will always get easy cubics and thus you will always be able to find one factor!!

In this case, you can see that if a=1 the equation is equal so you realise that (a-1) is a factor.

now divide by (a-1) and you will get a quadratic which you can easily factorise again...

thx aloot ;D ;D
but isnt this a C2 question?
Title: Re: C2 DOUBT edexcel
Post by: past-papers on April 16, 2010, 03:57:10 pm
You tell me :P You asked it haha

It looks like a C2 but it's been more than 2 years since I did C2 so I can't be sure!!
Title: Re: C2 DOUBT edexcel
Post by: halosh92 on April 16, 2010, 03:59:59 pm
You tell me :P You asked it haha

It looks like a C2 but it's been more than 2 years since I did C2 so I can't be sure!!

haha lool no i didnt ask the question someone else did
XD thx alot anyways :) ;D ;D
Title: Re: C2 DOUBT edexcel
Post by: Amr Fouad on April 16, 2010, 04:06:09 pm
lool yes past papers is right..

firt you have to find the factors of the constant, in this case 30:

1,30,15,2,5,6,and the negatives of each..

and we know that (a+y) is a factor when f(-y) =0..therefore, a=1 obviously gives us zero,

and so (a-1) is a factor...

do long division, get the quadratic function, and find the solutions..

sorry 4 the late reply, i had to go lol ;D