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Edexcel FP3 - 27th June, 2016

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Reply 640

somevirtualguy

Pretty similar to the one that's causing trouble above, hope it helps....

Edit: Sorry about the orientation

(edited 7 years ago)

Reply 641

DrSerious

Original post by Inges

Anyone know where I can go from here? :/

Sorry, where are you trying to go? Reduction formula? I think this is similar to one in the book that I've done, I had to consider I(n+2), subtract them and use factor formulae.

Reply 642

Inges

Original post by somevirtualguy

Pretty similar to the one that's causing trouble above, hope it helps....

Edit: Sorry about the orientation

Thank you so much for this. I was wondering though, is re arranging and then proving it credible like that?
I always thought show that means get to that without using it?

Reply 643

Inges

Original post by DrSerious

Sorry, where are you trying to go? Reduction formula? I think this is similar to one in the book that I've done, I had to consider I(n+2), subtract them and use factor formulae.

So the first line is the answer, and the second line is what the question would be.

It is reduction formula yes, If you have another strategy for tacking these mofo's please do share :colondollar:

Reply 644

Major-fury

Original post by Inges

So the first line is the answer, and the second line is what the question would be.

It is reduction formula yes, If you have another strategy for tacking these mofo's please do share :colondollar:

try expanding cos(2x). we know from trig identities that cos(2x)=2cos^2(x)-1=1-2sin^2(x). also expand the sin(2x) oln the other side = 2sin(x)cos(x)

Reply 645

somevirtualguy

Original post by Inges

Thank you so much for this. I was wondering though, is re arranging and then proving it credible like that?
I always thought show that means get to that without using it?

Well, June 2011 question 8d was a loci question and it said to show some equation was the loci of the mid point of two points, but the mark scheme just plugged values into the left side of the equation and the right side and showed they were equal, which annoyed me when I'd properly derived it, they basically cheated. But if they do it for show that's, so can we I guess :smile:

Reply 646

Geraer100

Hi, guys just to make sure one thing, the direction of the line of intersection of two planes(one has equation r.a=b and the other r.c=d) is a x c?

And do we need to know how to use the right hand screw rule, because I am a bit confused with this rule?

Thanks in advance!

Reply 647

somevirtualguy

Original post by Geraer100

Yes as the line of intersection will be perpendicular to both planes, so you need to cross product both their normal vectors to obtain the line's direction.

Reply 648

Geraer100

Original post by somevirtualguy

Yes as the line of intersection will be perpendicular to both planes, so you need to cross product both their normal vectors to obtain the line's direction.

Thanks!
And the right hand rule is it necessary to learn?

Reply 649

Armpits

Original post by Inges

So the first line is the answer, and the second line is what the question would be.

It is reduction formula yes, If you have another strategy for tacking these mofo's please do share :colondollar:

Thanks for that integral, was short but very fun!

Reply 650

Major-fury

Original post by Armpits

Thanks for that integral, was short but very fun!

no problem glad to help if possible could you post your own questions you find tough / tricky

Reply 651

Armpits

Original post by Major-fury

no problem glad to help if possible could you post your own questions you find tough / tricky

Never really seen a tough FP3 question tbh.

Though, if you haven't done some of the loci questions in June 14 and 15 I'd recommend it.

Reply 652

Hineshtailor

Original post by Armpits

Never really seen a tough FP3 question tbh.

Though, if you haven't done some of the loci questions in June 14 and 15 I'd recommend it.

yu know how to do question 8 on june 2015?

Reply 653

Armpits

Original post by Hineshtailor

yu know how to do question 8 on june 2015?

Yeah, any part you'd like to discuss?

Reply 654

Hineshtailor

literally all of part B and C lol. what is the eccentricity rule?

Reply 655

Armpits

Original post by Hineshtailor

literally all of part B and C lol. what is the eccentricity rule?

b)
Distance between a general point and the focus divided by the distance between the directrix and that same general point, equals eccentricity.

So you do PF/PD ( D=Directrix) = e

PF = PDe

You can work out PD and e from the information above and the modulus sign just means to ignore the negative sign.

You'll find that it adds up to 4.

(edited 7 years ago)

Reply 656

Armpits

Original post by Hineshtailor

literally all of part B and C lol. what is the eccentricity rule?

c)Chord touches two sides of an ellipse so you can label each of these point A and B.

They'll have coordinates: A (a cosθ, b sinθ ) and B(a cosp, b sinp )

All parallel chords will have the same gradient so you can just consider these two points.

Work out the gradient of the line joining A and B, call that m.

Use one of thes rules on pg 8 of this: https://qualifications.pearson.com/content/dam/pdf/A%20Level/Mathematics/2013/Specification%20and%20sample%20assessments/N38210A-GCE-Mathematical-Formulae-Statistical-Tables.pdf

To transform the gradient into a form which has cos and sin multiplied together.

Use A and B to calculate general midpoint.

General line will have equation y= mx (c = 0 since the line goes through all chords, there must be a chord through (0,0) )

So you can divide the y value from the midpoint and x value from the midpoint, to get y/x = m, then rearrange and use the gradient to get y = -1/4m

Reply 657

TheMarshmallows

Original post by Hineshtailor

literally all of part B and C lol. what is the eccentricity rule?

part B:

Use general point of an ellipse and foci from part a with Pythagoras (if you don't know eccentricity rule)

part C:

consider a line y=mx+c,
sub into ellipse to find where it hits it as a quadratic in terms of x
find x-coord of midpoint of the line between those two points
write it as c=something (will be in terms of m and x) then sub back into y = mx+c and simplify.