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# Edexcel C3,C4 June 2013 Thread watch

1. (Original post by masryboy94)
i am abit confused at working out
Try and use trig identities to represent the integral in terms of either sin or cosine to only the 1st power
2. (Original post by browb003)
Try and use trig identities to represent the integral in terms of either sin or cosine to only the 1st power
i think i did try that but couldn't get to the answer
3. (Original post by masryboy94)
i think i did try that but couldn't get to the answer
What's the answer that's given? I'll have a go at it and see what I get
4. (Original post by browb003)
What's the answer that's given? I'll have a go at it and see what I get
5. (Original post by justinawe)
He applied the chain rule incorrectly, so if you followed his working you'd get the wrong answer.
question 34 mixed exercise L integration, the last question, I think there is a mistake , because A should be -27, as you are multiplying 9 with -3
6. (Original post by strawberri)
I don't NEED an a* but would like one as it would enable me to get a grant if I got two other As..
unfortunately I got 80ums in C3 which means I have to get 100ums/full marks in C4 to get an A*!!! ermmm....

(I'm not re-taking C3 as I do French and there are no January A2 exams so everything rests on the summer ones...)
What's the workload like for French A2? possible to self teach? with AS?
7. for c4 do we need to be able to determine the nature of turning points? for implicit / parametric differentiation?
8. (Original post by otrivine)
question 34 mixed exercise L integration, the last question, I think there is a mistake , because A should be -27, as you are multiplying 9 with -3
You can't have a negative area.
9. (Original post by justinawe)
You can't have a negative area.
so they ignored the minus sign
10. Is it just me or is C4 so much nicer than C3?! DX
11. (Original post by masryboy94)
You can rewrite the integrand as sin(x)^2 - sin(x)^4

sin(x)^2 integrates to: x/2 - sin(2x)/4 (+c)

sin(x)^4 integrates to: 3x/8 - sin(2x)/4 + sin(4x)/32 (+c)

You get this answer if you rewrite cos(x)^2 = 1 - sin(x)^2
in the first line. Of course you can rewrite the integrand in terms of cosine as well and get an answer that looks different, but should be equivalent mathematically
12. (Original post by browb003)
You can rewrite the integrand as sin(x)^2 - sin(x)^4

sin(x)^2 integrates to: x/2 - sin(2x)/4 (+c)

sin(x)^4 integrates to: 3x/8 - sin(2x)/4 + sin(4x)/32 (+c)

You get this answer if you rewrite cos(x)^2 = 1 - sin(x)^2
in the first line. Of course you can rewrite the integrand in terms of cosine as well and get an answer that looks different, but should be equivalent mathematically
sorry i lost you on the first part, what is it that you rewrote? and where did you get -sinx^4?
13. (Original post by masryboy94)
sorry i lost you on the first part, what is it that you rewrote? and where did you get -sinx^4?

and then you can use the identity several times in order to get everything to the 1st power
14. (Original post by masryboy94)
i am abit confused at working out
this might be an easier way:

use the identities and

therefore the equation can be written as

simplify and then expand the brackets above: =

use the identity: therefore and subbing this into the original equation:

multiply the brackets above and simplifying:

now integrate:
15. sorry but question 30)a) mixed exercise L intrgration,

I differentiated u=1+2x2

and got dx=1/4x du

in the book they did

x dx = 1/4 du ?

what?
16. (Original post by otrivine)
sorry but question 30)a) mixed exercise L intrgration,

I differentiated u=1+2x2

and got dx=1/4x du

in the book they did

x dx = 1/4 du ?

what?

17. (Original post by browb003)

and then you can use the identity several times in order to get everything to the 1st power
(Original post by gaffer dean)
this might be an easier way:

use the identities and
therefore the equation can be written as

simplify and then expand the brackets above: =

use the identity: therefore and subbing this into the original equation:

multiply the brackets above and simplifying:

now integrate:
thank you both !!! now i get it
18. (Original post by browb003)

is it because they do not want to include x so they can cancel things because everything is in terms of u?
19. (Original post by otrivine)
is it because they do not want to include x so they can cancel things because everything is in terms of u?
Yeah, as rewriting everything in terms of u when substituting will result (in this case) in an integrand that is much easier to integrate
20. (Original post by masryboy94)
thank you both !!! now i get it
It's important to Remember these identities:
, ,

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