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OCR MEI - C1 - 13th May 2015

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Hey all, I'm one of those that'll keep the grade boundaries low for you :P yep there are plenty of us so don't worry.

Just asking because I keep forgetting, for what reasons do you need to work out the discriminant and when the d2y÷dx2? Keep getting it the wrong way round.

Also for the discriminant, is it positive or negative that has 0 or 2 real roots?
Original post by xoharrypotter
Find the set of values of k for which the graph of y=x^2+2kx+5 does not intersect the x axis.

So did:
b^2-4ac

2k^2-4x1x5<0
2k^2-20<0
2k^2<20
k^2<10
k<root10

According to the markscheme i would of gotten 3/4 but not 4/4 because when you sub in the equation to b^2-4ac you sub 4k^2 not 2k^2

Why would it be 4 and not 2 since 2 is in the equation right?
Thank you

my only issue is how did u get 2k^2-4x1x5 from y=x^2+2kx+5
Original post by Velocity_
my only issue is how did u get 2k^2-4x1x5 from y=x^2+2kx+5


a=1 b=2k c=5 , so b^2 - 4ac will be (2k)^2 - (4x1x5)
[QUOTE="micaela_m;55718741"]
Original post by AbdulArshad

Yeah thank you, I'm just doing that paper now, I've done it before but it was a while back. Thanks for your help!! Good luck if you're doing the exam tomorrow :tongue:


Anytime! Good luck tomorrow :smile:! You'll smash it :smile:
Original post by climatechange101
thank youuuu xxx i really needed some motivation xxx


You'll do great tomorrow! Good luck :smile:


Posted from TSR Mobile
Good luck tomorrow everyone :smile: you'll all do great!
Good luck
Original post by Jablonski
Hey all, I'm one of those that'll keep the grade boundaries low for you :P yep there are plenty of us so don't worry.

Just asking because I keep forgetting, for what reasons do you need to work out the discriminant and when the d2y÷dx2? Keep getting it the wrong way round.

Also for the discriminant, is it positive or negative that has 0 or 2 real roots?



Discriminant b^2-4ac is used to find how many roots a quadratic has (how many times it crosses the x axis)
>0 means 2 real roots
=0 means 1 equal root
<0 means no real roots

You do d^2y/dx^2 to find whether a stationary point (where dy/dx = 0) is a maximum or minimumD^2y/dx^2 > 0 means it is minimum
D^2y/dx^2 < 0 means maximum

Hope this helps
Reply 88
Avatar for Rik21
Rik21
2
Original post by Brian luiz
Discriminant b^2-4ac is used to find how many roots a quadratic has (how many times it crosses the x axis)
>0 means 2 real roots
=0 means 1 equal root
<0 means no real roots

You do d^2y/dx^2 to find whether a stationary point (where dy/dx = 0) is a maximum or minimumD^2y/dx^2 > 0 means it is minimum
D^2y/dx^2 < 0 means maximum

Hope this helps


Differentiation is not in C1 is it? :redface:
Reply 89
Avatar for Rik21
Rik21
2
Original post by AlexParmenter
I can't find the exact question but if you have a circle equation and the equation of a tangent, how do you find the equation of the other parallel tangent? Obviously you have the gradient but what point would you sub in? Thanks

Need to sleep soon so this will be brief
Basically the point A is a number of x and y away from the centre of the circle
so say if x increases by 1 and y increases by 2 (to get A from the centre)
To get B (where there is a parallel tangent to A) you get the centre of the circle and decrease x by 1 and decrease y by 2
Can someone pls guide me through Q13 on JUN 2006
Original post by ALEVELMASTER110
Can someone pls guide me through Q13 on JUN 2006


LOL LOL someone needs to slap me, I bloody hate it when I don't read the question and as a result misinterpret it. One piece of friendly advice for tomorrow fellow students; read the question twice before even putting your pen on the paper, even if the question is like work out x from 2x-2=0.

Cheers and Good Luck

:smile:
Reply 92
Avatar for DaGuy
DaGuy
2
Good Luck everyone. Hope for a good paper!
Original post by Rik21
Need to sleep soon so this will be brief
Basically the point A is a number of x and y away from the centre of the circle
so say if x increases by 1 and y increases by 2 (to get A from the centre)
To get B (where there is a parallel tangent to A) you get the centre of the circle and decrease x by 1 and decrease y by 2


Awesome, thanks! Good luck everyone!
Advice everyone who panics easily not to come on tsr after the exam last year I did and it affected a lot of my exams after because talking about the answers 😭
(edited 8 years ago)
just done the exam, found it pretty easy tbh. I got the infamous question 12 I unlike most of my friends. your opinions
Just sat the paper and it was absolute hell!
Hardest C1 paper I have ever done
Found that pretty easy, hopefully got 100% UMS.
Reply 98
Avatar for ebally
ebally
5
eh, was okay... think I made a silly mistake on Q6.ii)..the 32 over root 2 one and maybe Q12.i).
Oh well, not bad over all, hopefully high A! :biggrin:
32 over root 2 had to be timed by root two over root two. overall, the paper was easy

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