**HL Maths P2 Before/After

Mista

Hayezer wrote: »

I tried emperical rule for all that question stupidly. Mean was 20, SD 0.10 and limit was 19.75-20.25. So I thought it was 2.5 standard deviations from the mean which is 97.35. So I thought that leaves 2.35% of faulty batteries, so I multiplied 0.0235 by 10,000 and got 235 (wrong :L). If any of that makes sense :L.

Hopefully a few attempt marks

Nah, ye had to use z-scores.. but you'll get a good few attempt marks I'd say..

When it asked for the percentage increase, did it mean just your new answer minus your old one?

Chuchoter

I got some ridiculous 300% increase for the battery question. :P

Mista

mathstalk wrote: »

Need to know: Did anybody else get 2+root(2) for k?
Also, did anybody else's graph end up as a half doughnut?

Yes, and yes.. not confident of the k part though, thats the first person I've seen with that answer

tanzy

I wanted to ask if people got something like this for the last part of question 8?

jos360

ei.sderob wrote: »

Even though it said K>1 I'm almost positive my method was right.

Lots of people did this and got k=1
This happened because you left the radius as r or whatever when you were working out. But if you do a little bit of geometry you find that r=a quadratic equation. From the quadratic you get two values for r and I think you had to use both of them in your further workings. If you only use one value for r they cancel each other and you get 2=2k and then k=1.
You were probably on the right track, you just had to find an two expressions for r (I think they were conjugates) and work with those and not just with the letter 'r'.

I'm not fully sure if Im right tho but it seems logical to me (although Im not explaining it very well)

GiveEmHellKid

Personally I was fine until question 6. I hadn't the foggiest what was going on in q8. I got beta to be 80 and alpha to be 48 methinks.
I've honestly never seen so many people cry after a single exam. It was quite the odd one.

Osric

I did simultaneous equations in g, and got k=5.828

I used the fact that the midpoint (1,1) of the line segment on x+y=2, from the y-intercept (0,2) to the x-intercept (2,0), is on the circle. Then the equation of the diameter/radius is x=y (can be proven using perpendicular slope), so g=f. Since the graph is touching both axes, g^2=c. From that I solved for g, and took the bigger answer (g=radius, so smaller answer would give a tiny circle). Then used perpendicular distance formula from (1,1) to the other line, and got k=5.828, or k is negative

Hayezer

I really regret not trying the last 2 bits of Q8 . Was there any actual maths in the graph part of 8? I just saw it and got confused and left it

RedTexan

mathstalk wrote: »

Need to know: Did anybody else get 2+root(2) for k?
Also, did anybody else's graph end up as a half doughnut?

I think that was the answer for the radius of the circle and the centre co-ordinates (which would be the same with x and y axis tangents) and for the robotic arm, yeah a half doughnut but with a bit under on the right hand side

mathstalk

tanzy wrote: »

I wanted to ask if people got something like this for the last part of question 8?

No, I got something like this:

Rebels101

mathstalk wrote: »

Need to know: Did anybody else get 2+root(2) for k?
Also, did anybody else's graph end up as a half doughnut?

ya i got 2+root2 as well! i think its right!

RedTexan

Osric wrote: »

I did simultaneous equations in g, and got k=5.828

that's what I got too, you confident? :P

jos360

Mista wrote: »

Yes, and yes.. not confident of the k part though, thats the first person I've seen with that answer

Your graph bit is definitely right where the outer arcs radius is the sum of the two arms (or the length of the arm fully extended) and the inner arcs radius is the difference of the length of the two arms). They left a trap in that tho, if you drew the full circle (360 deg) its not right because you're told the max angle is 180 deg

For the K part, I can't fully remember what I did (did this question first) but I graphed it after and I'm pretty sure I was right.
And yea I think I came across a 2+root2 and a 2-root2 somewhere.
You needed the conjugate roots for r so you could use the two different values otherwise they just canceled each other in the main equation and you would get k=1 (which you are told is untrue)

MattHelders

mathstalk wrote: »

No, I got something like this:

Not sure if you intentionally made it look like a penis but mine was quite similiar

mathstalk

Rebels101 wrote: »

ya i got 2+root2 as well! i think its right!

Yes! And did you use co-ordinate geometry? I used plain geometry and trigonometry: Sine Rule, Cos Rule bla bla bla...

ChemHickey

Aww I was happy with maths, some parts were hard but I think I read the last graph wrong with the robot arm. Kinda p*ssed now if that costs me the a1. I read it as the points where the robotic arm passes through, so I shaded the whole weird figure instead of the rainbow and tail. I hope my paper 1 will throw me up to the a1... grrr.

RedTexan

tanzy wrote: »

I wanted to ask if people got something like this for the last part of question 8?

Kind of, I think that's a little more correct than my answer, what did ye say for the first part, a degree error in alpha or beta and for what reason?

DepoProvera

ChemHickey wrote: »

Aww I was happy with maths, some parts were hard but I think I read the last graph wrong with the robot arm. Kinda p*ssed now if that costs me the a1. I read it as the points where the robotic arm passes through, so I shaded the whole weird figure instead of the rainbow and tail. I hope my paper 1 will throw me up to the a1... grrr.

It was 1/4 of a 75 mark question so it was probably worth around 20 marks.. and you probably got 10/20 of them :L It's grand brav

Osric

RedTexan wrote: »

that's what I got too, you confident? :P

Everyone is getting different answers, so no

mathstalk

MattHelders wrote: »

Not sure if you intentionally made it look like a penis but mine was quite similiar

Haha, no just a quick paint job. Somebody definitely should have done that in the exam though. XD

RedTexan

Osric wrote: »

Everyone is getting different answers, so no

well I got k=1 and that and then discarded 1

Spattersonox

tanzy wrote: »

I wanted to ask if people got something like this for the last part of question 8?

LOL.. guess I just lost twenty marks :L

montown

did anyone else interpret the first question about the parallelogram as 3 ways to distinguish a parallelogram from a square/rectangle? i didnt write opposite sides equal or opposite angles equal because i thought it was asking for something that distinguishes a parallelogram from other quadrilaterals

ChemHickey

DepoProvera wrote: »

ChemHickey wrote: »

Aww I was happy with maths, some parts were hard but I think I read the last graph wrong with the robot arm. Kinda p*ssed now if that costs me the a1. I read it as the points where the robotic arm passes through, so I shaded the whole weird figure instead of the rainbow and tail. I hope my paper 1 will throw me up to the a1... grrr.

It was 1/4 of a 75 mark question so it was probably worth around 20 marks.. and you probably got 10/20 of them :L It's grand brav

I hope so. i got the tail, and I knew what to do, it was just the stupid shading. Thanks for the consolation.

Osric

Anyone do 6B, the one with the incircle angle proof?

RedTexan

DepoProvera wrote: »

It was 1/4 of a 75 mark question so it was probably worth around 20 marks.. and you probably got 10/20 of them :L It's grand brav

well last year they had a question like that at the end and only gave it 5 marks. For the parts previous would it be correct to go on about if the distance between P and R was greater than 12 then the change in alpha would cause a greater change in the position of R because it was an arc with a larger radius and so on?

Rebels101

mathstalk wrote: »

Yes! And did you use co-ordinate geometry? I used plain geometry and trigonometry: Sine Rule, Cos Rule bla bla bla...

I used co-ordinate geometry said since the circle is tangent to x and y the centre must be (x,y) but also x equals y! then i did perpendicular distance formula from centre to line and got k=1 or k=2+root2 so took the second one!

Mista

montown wrote: »

did anyone else interpret the first question about the parallelogram as 3 ways to distinguish a parallelogram from a square/rectangle? i didnt write opposite sides equal or opposite angles equal because i thought it was asking for something that distinguishes a parallelogram from other quadrilaterals

Squares and rectangles are parallelograms?

DesmondGAF

Chuchoter wrote: »

I got some ridiculous 300% increase for the battery question. :P

I got 387% or something :cool:

ferike1

reznov wrote: »

Yeah considering the fact that there was more writing than mathematics. How can you learn Maths off? Lmao. As the independent wrote - "common sense and general knowledge". Doesn't equate to Maths.

Surely people doing honours maths have plenty of common sense and general knowledge.

Learning maths off = doing equations, sums etc and only knowing how to do a certain type of question. Understanding maths = knowing concepts and applying them to anything thrown at you.