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Edexcel A2 C3 Mathematics 12th June 2015

I don't follow :[

Sin(x+a) is exactly the same as sin(a+b) with x as a and alpha as b. You can therefore use the normal formula to expand it

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Reply 721

aersh8

14

Original post by samb1234

You would risk losing marks. No point in doing that really not like it takes long to write it out (especially if you made a stupid mistake you would get 0)

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I've never done it any other way (so don't even know how I should write it out), and I always plug in some numbers to check whether I get the same answer...

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Reply 722

pearl_rose

16

Original post by samb1234

Sin(x+a) is exactly the same as sin(a+b) with x as a and alpha as b. You can therefore use the normal formula to expand it

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Ohhh haha thanks

Reply 723

aersh8

14

Original post by samb1234

You would risk losing marks. No point in doing that really not like it takes long to write it out (especially if you made a stupid mistake you would get 0)

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Just checked the 2013 and 2014 mark schemes - the method marks are given for what I do (r^2 = coefficient ^2 + coefficient ^2 and tana = (coefficient/coefficicient) so I guess it's fine :biggrin:

Reply 724

samb1234

13

Original post by aersh8

Just checked the 2013 and 2014 mark schemes - the method marks are given for what I do (r^2 = coefficient ^2 + coefficient ^2 and tana = (coefficient/coefficicient) so I guess it's fine :biggrin:

Then you'll be fine then. Both methods are correct I just tend to write it out as I have enough time and means I am more careful (I obviously plug numbers in as well just to be safe)

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Reply 725

pearl_rose

16

Original post by samb1234

Rsin(x+a) expand sin(x+a) and do coefficient matching eg if you had 7sinx + 4cosx then when you expand rsin(x+a) you would get Rsinxcosa +rsinacosx. By matching the coefficients of the two, you can say that rcosa =7 and rsina=4. Then you can divide the two to get tan a. R is basically coefficient if sin squared plus coefficient of cos squared all rooted. For us it normally tells you its positive but just be careful as it could be -ve. To get the two identities you just divide by either sin^2 or cos^2

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Ok so all in all which identities do you think you need to have memorized and that you can't derive from the formula sheet? Thxx

Reply 726

Efemena15

4

I hope we're not asked to draw graphs of cot, sec or cosec

Reply 727

randlemcmurphy

11

Original post by Efemena15

I hope we're not asked to draw graphs of cot, sec or cosec

I'm more worried about being asked to draw the graphs of arcsin, arccos and arctan and having to remember the domain and range for each graph.

Reply 728

Kevin De Bruyne

21

Original post by randlemcmurphy

I'm more worried about being asked to draw the graphs of arcsin, arccos and arctan and having to remember the domain and range for each graph.

Remember that for drawing those you can't have the same y value pop up on the graph twice, and that arcsin, arccos and arctan are the inverse functions of sin, cos and tan. So for arcsin and arccos the domain, i.e what you put in, will be between 1 and -1. This makes sense because the range of sin and cos are -1 and 1. The range is the domain of sin and cos, so at -1 it'll be -pi/2 and -pi respectively, and at 1 it will be pi/2 and 0 respectively. I can't remember much about arctan but I vaguely remember the shape of the graph and it shouldn't be too difficult.

Reply 729

cerlohee

16

Hi everyone, so I'm having trouble with this question: http://gyazo.com/1f59f436bde2776d6d038bd313fc4e39
For part C, I have worked out that b is 6, how do I then go onto work out A? I got 1/5th... Thanks

(edited 8 years ago)

Reply 730

samb1234

13

Original post by cerlohee

Hi everyone, so I'm having trouble with this question: http://i.gyazo.com/90da8d80d402473cdbbd213855aedf55.png
I have worked out that b is 6, how do I then go onto work out A? Thanks

ALSO this question: http://i.gyazo.com/893eaaf9bd27c4b0a02a8512344a0a6c.png
I got a max value of 1.107 by making 100sinsq(theta-1.107)=0??

I'm sorry I need to do some revision for chemistry otherwise I would do it for you. Just some advice, it would help if you posted the full questions as you can only see the specific part of the question, not the rest of it (or is that just me?)

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Reply 731

MiloHVLeonard

1

Hey guys,
Do we need to know proof by contradiction, exhaustion, and counter example?
One of my friends said he saw it in his CGP book, and I saw proof by counter example in a solomon paper, but it says nothing on the spec
I'm pretty sure that we don't need to know, but I just want to make sure
Does anyone know?
Thanks

Reply 732

cerlohee

16

Original post by samb1234

I'm sorry I need to do some revision for chemistry otherwise I would do it for you. Just some advice, it would help if you posted the full questions as you can only see the specific part of the question, not the rest of it (or is that just me?)

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Ah sorry no wonder I've had no replies!
Have fixed it now if anyone can help out. Have fun with chemistry :smile:

Reply 733

s.c.a1

10

can someone pls help me with this question. why is part b a quadratic equation?? why cant i just ln the whole thing

Screen Shot 2015-05-30 at 16.41.40.png105.1KB

Screen Shot 2015-05-30 at 16.41.15.png93.7KB

Screen Shot 2015-05-30 at 16.42.01.png118.2KB

Reply 734

yelllowribbon

13

Original post by MiloHVLeonard

Hey guys,
Do we need to know proof by contradiction, exhaustion, and counter example?
One of my friends said he saw it in his CGP book, and I saw proof by counter example in a solomon paper, but it says nothing on the spec
I'm pretty sure that we don't need to know, but I just want to make sure
Does anyone know?
Thanks

Pretty sure we don't need it...but yeah check with someones else, or on the spec

Reply 735

studentwiz

3

Original post by s.c.a1

can someone pls help me with this question. why is part b a quadratic equation?? why cant i just ln the whole thing

let e^x = y

y-3/y=4 xboth sides by y

y^2+3=4y rearrange ...y^2-4y+3=0 solve for y then sub into e^x=y to find x values

Reply 736

studentwiz

3

Original post by cerlohee

Ah sorry no wonder I've had no replies!
Have fixed it now if anyone can help out. Have fun with chemistry :smile:

coordinates (6,-1)

a l6-bl -1 = -1
a l6-bl =0
divide by a
6-b=0
b=6

Reply 737

mismash

2

hello, i am really sorry to but in.. but im a year 12 student and i am really worried because i dont think i have done v well in my c1 and c2 maths exams.
would u guys recommend retaking those modules in y13 or simply is it going to waste time and increase work load too much...???

Reply 738

randlemcmurphy

11

Original post by cerlohee

Hi everyone, so I'm having trouble with this question: http://gyazo.com/1f59f436bde2776d6d038bd313fc4e39
For part C, I have worked out that b is 6, how do I then go onto work out A? I got 1/5th... Thanks

We know two points so we can form two equations:

1=a|6-b|-1This means a|6-b|=0 So a could equal zero and b could equal 6

We also have:

11=a|0-b|-1This means ab=12
This means that a cannot equal zero, so b equals 6 and a equals 2 (hope that is the right answer!)

(edited 8 years ago)

Reply 739

lam12

2

Original post by cerlohee

Ah sorry no wonder I've had no replies!
Have fixed it now if anyone can help out. Have fun with chemistry :smile:

The range changes because it's 3theta. You use 2pi... I don't exactly know what you're exactly asking tbh haha

For the first bit because it's a ^2 it can't be a negative and therefore the sin bit = 0

For the second part it would be 3 theta - 1.107 = 2pi as the range increases as its 3theta and now we can go up to 3pi but it's not = to 3pi and therefore we use just 2pi

I don't think I explained this well but I tried, I may be wrong but it's how it was explained to me :-)

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Edexcel A2 C3 Mathematics 12th June 2015

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