WJEC C4 17th June 2016

Original post by Jack1066

I found that decent. Some tough ones on there definitely.

I reckon ~55 for an A.

Binomial I got 1/10 for the 2nd bit.

The one with Tan and cot I got 56.9 degrees, 60 something and 1 hundred and something.

For the point P at (1,9) I got 9/2 and 3/2 as values for P

Vector value P I got 10.

The diff equation I messed up part c completely. That was tough.

Yep these are all correct.

Reply 42

Original post by thad33

I got the same but you factorise it to get x^2(x^2 - 2) + 1 is less than zero so you just have to explain that all the values are positive so it must be greater than zero hence the contradiction

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I did it slightly differently, took the 1 over the other side to -1. Then said how x⁴ and x² are always positive so x was not real ( contradiction)

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Reply 43

Original post by 98matt

I did it slightly differently, took the 1 over the other side to -1. Then said how x⁴ and x² are always positive so x was not real ( contradiction)

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You're probably more right than what I put. I was sweating by the end of it thinking I ****ed up so wasn't thinking straight.

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Reply 44

Original post by thad33

Yeah I got the same. Tbh apart from the proof by contradiction question the whole paper was harder than last year I think

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I think that it was possibly the easiest one I've seen...
They give you the hint that you start by squaring, so

(x+1/x)^2<4
x^2+1/x^2+2<4
x^2+1/x^2-2=(x-1/x)^2<0 contradiction.

(edited 7 years ago)

Reply 45

Original post by IrrationalRoot

I think that it was possibly the easiest one I've seen...
They give you the hint that you start by squaring, so

(x+1/x)^2<4
x^2+1/x^2+2<4
x^2+1/x^2-2=(x-1/x)^2<0 contradiction.

Yeah I meant that the proof was easier than last years but on the whole it was on par if not harder.

I think they've given up asking hard vector questions now as well.

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Reply 46

Original post by thad33

Yeah I meant that the proof was easier than last years but on the whole it was on par if not harder.

I think they've given up asking hard vector questions now as well.

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When we did the paper checks and I saw an easy vectors I was like "there is still hope" ahahah

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Reply 47

Hopefulmedic15

x^4 - 2x^2 + 1 factorises to give

(x^2-1)^2<0 which contradicts that x is real

Reply 48

Original post by 98matt

When we did the paper checks and I saw an easy vectors I was like "there is still hope" ahahah

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I finished in an hour and literally had about 30 marks yet to answer and panicked so bad. Managed to get everything answered in the end but that vectors question was a dream.

I've realised I ****ed the contradiction up but it's only 2 marks lost.

How do you think C3 went?

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Reply 49

Original post by thad33

I saw Mathemateg's c3 markscheme. I think I got 68 or 69 /75. I panicked on the circles question and didn't spot it was simple SOHCAHTOA :frown:

I think c4 went a little better for me today - does anyone know if mathemateg will be doing a markscheme this afternoon or not until Monday?

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Reply 50

aehr

Original post by thad33

The -2 gradient spat out y=0 and x^2 = -4y^3.

You ignored the x value and plugged in y=0 into original equation, that gave you x^4= 16 which is plus/minus 2 so coordinates (-2,0) (2,0)

I think that was correct.

Agreed though, tough paper but hopefully the lower boundaries push my grades up.

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what do you mean spat out?
i put the gradient equal to -2 and rearranged it but couldnt work out how to separate the x and y terms :/

Reply 51

Original post by aehr

what do you mean spat out?
i put the gradient equal to -2 and rearranged it but couldnt work out how to separate the x and y terms :/

Yeh he's right (I think). One of the terms was the same on both sides and it cancelled. You had to factorise out the 3y in order to separate the terms. I got to 3y=0 but thought that was trivial so didn't plug it in to the original eqn :frown:

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Reply 52

aehr

I got t = 8 years on the differential equations Q but a few of you have said it was 10 :/ how did you get it?

Reply 53

EJRicketts

Original post by 98matt

Agreed ahahaha. I really hope mathemateg's mark scheme is up today

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Agreed

Reply 54

Original post by aehr

I got t = 8 years on the differential equations Q but a few of you have said it was 10 :/ how did you get it?

I first worked out b= 1.5, I don't think that was necessary though. Then I stuck in (A/4)² = A²/1.5t+1

I divided through by A², did a bit of rearranging and got t=10

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Reply 55

Original post by aehr

what do you mean spat out?
i put the gradient equal to -2 and rearranged it but couldnt work out how to separate the x and y terms :/

When you rearranged the gradient = -2 you ended up with a few x and y terms which when factorised gave 3y( something else ) = 0 so y=0 was one. The other term had no solutions. Sub in y=0 into the original equation removed all y terms so you could work out x

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Reply 56

Original post by 98matt

I first worked out b= 1.5, I don't think that was necessary though. Then I stuck in (A/4)² = A²/1.5t+1

I divided through by A², did a bit of rearranging and got t=10

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I fluked that question. It just didn't click but managed to grind out t=10. I took like a whole page going round in circles

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Reply 57

Original post by thad33

You certainly would not just 'ignore the x value here'. y=0 is one solution, the other is the one in the bracket, which gave you x^2+4y^2=0 (not what you said) and you don't ignore this either, you have to say that this is not possible unless y=0.

Reply 58