Edexcel C3,C4 June 2013 Thread

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Reply 4620

m4ths/maths247

Original post by orange94

Hey what did I do wrong with this question!! Help !!

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Nothing, 1 is a constant, c is a constant.
Let them get married :lovie:

Reply 4621

Zazuwaved

Original post by Myocardium

How would you integrate something like 3^x?

3^x/ln(3) + c

Reply 4622

Myocardium

Original post by PythianLegume

Hence integrating 3^x leads to division by ln(3).

Original post by Westeros

\int a^x = \frac{a^x} {\ln a} +C

Oh I see... What about something like 3^2x?

Reply 4623

PhoenixSeeker

Original post by PythianLegume

You've integrated it wrong - it looks more like differentiation there.

Ahh brilliant thank you :smile:

Reply 4624

jadecross

Original post by Westeros

The half angle is because you have cos x
So to be able to use the double angle formulae, x must be x/2
so cos2(x/2) = cos x

Original post by justinawe

You want to get rid of the square root, so you need it in terms of something squared.

\sqrt{2 - 2\cos x}

= \sqrt{2 - 2(1 - 2\sin^2 \frac{x}{2})}

= \sqrt{2 -2 + 4\sin^2 \frac{x}{2}}

= \sqrt{4\sin^2 \frac{x}{2}}

= 2\sin \frac{x}{2}

thank you guys, thank you Justin that makes more sense now :smile:

Reply 4625

PhoenixSeeker

Does anyone have a copy of the leaked June 2012 C4 Paper and mark scheme?

Reply 4626

Westeros

Original post by lefterispower

please guys i want help with the question 7 c) in the paper of January 2013... :frown:

What don't you understand?

Tip: If you're told that AP is perpendicular to l1, then the dot product must equal 0

Reply 4627

kitty-boo

arrrrgh! integration is a disaster. :cry:

Could somebody please explain integration in brief? ASAP! thanks !

Reply 4628

justinawe

Original post by Myocardium

Oh I see... What about something like 3^2x?

Unparseable latex formula:

3^2^x = (3^2)^x = 9^x

Reply 4629

username878045

Original post by Myocardium

Oh I see... What about something like 3^2x?

Well y=3^2x

ln(y) = 2xln(3)
(1/y)(dy/dx)=2ln(3)
dy/dx=2 x 3^2xln(3)

Hence integration divides by 2ln(3).

Reply 4630

Dev607

When do you use radians or degrees if the question doesn't tell you??

For example in this question part e (http://gyazo.com/06b6e38f7d8f889efc89c4e44c5478fe) I used degrees and I got the wrong answer. You had to use radians, but it didn't specify it anywhere.

Reply 4631

orange94

Original post by sonyeric33

u forgot to find du/dx and sub that in

You mean like this ?

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Reply 4632

nm786

Original post by PhoenixSeeker

Does anyone have a copy of the leaked June 2012 C4 Paper and mark scheme?

Paper: http://www.thestudentroom.co.uk/attachment.php?attachmentid=218600&d=1369299971

Mark Scheme: http://www.thestudentroom.co.uk/attachment.php?attachmentid=218597&d=1369299296

Reply 4633

Kardy

Original post by lefterispower

please guys i want help with the question 7 c) in the paper of January 2013... :frown:

Form simultaneous equations to find lamda. The two equations can be formed from the dot product of l1 & AP (which are perpendicular so = 0 ) and the other equation you already have, it's the equation of the line l1.

http://www.examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=407&solution=7.3

Reply 4634

DELETED ACCOUNT

Original post by ytop2

can ANYONE please help me solve this equation to get it in terms of V, as I have put at the side :frown:

can't do it at all

Multiply by k, Take exponentials, Get rid of the denominator by multiplying through, Expand brackets and take it from there.

Reply 4635

username878045

Original post by Dev607

With integration and differentiation, it's generally radians. Also, think about the values in that question - if it asks about 2 weeks, when t=2, you're not going to be doing sin of 1 degree.