OCR MEI C4 - June 13th 2011

cot^2(t)-2cot(t)=0

You multiplied everything in line two by tan^3(t)? That's just gonna generate other results. Substitute t = 0 (tan(t) = 0) into the original:

cosec^2(x) = 1 + 2cotx

It doesn't work.

I cross multiplied.

Reply 381

viksta1000

15

Original post by emyholdem

For the cosec question i got theta to equal -180, 0, 180, and around 50ish, and -130ish.

The reason i got theta=0 is

it was along the lines of...

cot^2(t)-cot(t)=0

I got to this bit and then factorised

cot(t) [(cot(t) - 1]

so cot(t) = 0 or cot(t) =1

cot(t) = cos(t)/sin(t) so cos(t) = 0 (as denominator cannot =0) so t= -90, 90

then the other one

cot(t) = 1 so cos(t)/sin(t) = 1, so sin(t)/cos(t) = 1, so tan(t) = 1, so t = -135, 45

how many marks do you reckon i'll get?

Reply 382

Reminisce

11

Okay for those who put 180, 0, -180, 90 or -90,

try ALL of them in the original equation:

cosec^2(x) = 1 + 2cot(x)

They don't work.

Reply 383

bear54

Original post by Reminisce

Okay for those who put 180, 0, -180, 90 or -90,

try ALL of them in the original equation:

cosec^2(x) = 1 + 2cot(x)

They don't work.

How many marks are lost for extra answers?

Reply 384

tsr4life

2

i hated that paper...SO BAD!! i reckon i got somewhere around 70%...luckily i only need an average of 70% in both s2 and this and im also retaking c3 to boost up my mark.

for the vectors question, anyone know what the the vector of the horizontal plane was?? and how do you prove something is a trapezium??

one more question...you reckon we'll get any marks if we did if, for the table, we did 1% instead of 0.1%? seriously annoyed about that, should have checked more carefully

Reply 385

lydia1993

I thought the paper was okayy, paper A was fine, panicked a bit when i first saw 'coplanar' but realised it just meant on the same plane and managed to prove it was a trapezium fine. Thought the comprehension was a bit nasty, i havent done stats since last year and couldnt remember how to do question 2, tried doing nCr/nPr and put a final answer as 5000-and something. Knew it was too small though :/ i thought the rest of it was fine, the tables were nice as was the venn diagram :smile:

Reply 386

Wezzler

Original post by Reminisce

Everything is right apart from tanx = 0, it orginally had cotx = 0 you can't reciprocal 0.

yup that's right even though i did that in the exam :/ fml

Reply 387

englica

Original post by tsr4life

i hated that paper...SO BAD!! i reckon i got somewhere around 70%...luckily i only need an average of 70% in both s2 and this and im also retaking c3 to boost up my mark.

for the vectors question, anyone know what the the vector of the horizontal plane was?? and how do you prove something is a trapezium??

one more question...you reckon we'll get any marks if we did if, for the table, we did 1% instead of 0.1%? seriously annoyed about that, should have checked more carefully

I think to get the vector for the horizontal you had to choose any two points with the same z co-ordinate?

Reply 388

Reminisce

11

Original post by bear54

How many marks are lost for extra answers?

1 most likely, perhaps 2

It seemed deliberate to catch people out so I wouldn't think they'd let people off but you never know...

Reply 389

Reminisce

11

Original post by englica

I think to get the vector for the horizontal you had to choose any two points with the same z co-ordinate?

To be honest (0,0,1) would do.

(I assume you mean the question on finding the angle between two planes where you use the normals)

(edited 12 years ago)

Reply 390

luke-1234

Original post by Reminisce

To be honest (0,0,1) would do.

Wouldn't it be (1,1,0) though?

Reply 391

Reminisce

11

Original post by luke-1234

Wouldn't it be (1,1,0) though?

Look at my edit, I forgot to clarify :smile:

Reply 392

Wezzler

lol i got vector of horizontal plane completely wrong, think i put (-4,0,0) :/

Reply 393

emyholdem

Original post by luke-1234

Wouldn't it be (1,1,0) though?

Thats what i put, both would give the correct answer although only by complete fluke. however those that used (0,0,1) would have to do 180-their answer.

Only by complete fluke.

Reply 394

Reminisce

11

Original post by emyholdem

Thats what i put, both would give the correct answer although only by complete fluke. however those that used (0,0,1) would have to do 180-their answer.

Only by complete fluke.

Not really, two normals have an angle equal to the angle between two directions of the planes. i.e. both would be fine.

(edited 12 years ago)

Reply 395

luke-1234

Which answer is the fluke?

Reply 396

Ray_Han

11

Original post by emyholdem

Thats what i put, both would give the correct answer although only by complete fluke. however those that used (0,0,1) would have to do 180-their answer.

Only by complete fluke.

I did this- would I get the marks?
I think overall it was pretty tough paper, but hopefully I did well enough.
I'm a bit annoyed about the comprehension PIN number combination question, where I was out by one, and also I made a stupid error on the last question on the paper.

Reply 397

emyholdem

the dot product i calculated was (1,1,-2).(1,1,0). which gives 2.

However those that calculate (1,1,-2).(0.0.1) would get -2.

Those who got -2 would need to minus their angle from 180 i remember talking about it with my teacher.