Demento's Year 10 maths practice paper thread (1 Viewer)

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

???

x^2 + x + 2 = 0

(x+2) (x-1) = 0

x = -2, 1

There are roots.

its not x^2+x-2
it's x^2+x+2

I had a positive 2...

Or maybe i'm just blind.

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

Ah, minimum. Wasn't reading properly (sleep deprivation getting to me haha). In that case you do -b/2a for axis of symmetry and sub in for vertex.

Well it's already in the ax + bx + c form so why would we need to complete the square to find the minimum lmao

 

[Sy123]

Re: 2012 Year 9 &10 Mathematics Marathon

idgi

So the question gives you an equation. You factorise it and then you have to expand it again which gives you the same equation but the constant with a negative. If I factorise the new equation, I still get the same thing. I'm going in circles here.

The problem is you cant factorise it, take the discriminant:

1^2-4(2)=-7

So that means the discriminant is negative and means that there are no real roots. If you expand your answer again and you get something different to the question it means you did something wrong (assuming you expanded correctly)

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

The problem is you cant factorise it, take the discriminant:

1^2-4(2)=-7

So that means the discriminant is negative and means that there are no real roots. If you expand your answer again and you get something different to the question it means you did something wrong (assuming you expanded correctly)

What is the 'discriminant' and yes you can factorise x^2 + x -2 = 0? :s isn't it (x+2) (x-1)?

 

[HSC2014]

Re: 2012 Year 9 &10 Mathematics Marathon

I had a positive 2...

Or maybe i'm just blind.

Okay so x^2 + x + 2 = 0.
You factorised this into (x+2)(x-1) = 0
This part is already wrong (it is the factorisation of x^2 + x - 2, which is not the question)
I think this is what people have been trying to say?

 

[kazemagic]

Re: 2012 Year 9 &10 Mathematics Marathon

I had a positive 2...

Or maybe i'm just blind.

Yes it is positive 2. Tell me how do u factorise quadratics other than using completing square

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

Okay so x^2 + x + 2 = 0.
You factorised this into (x+2)(x-1) = 0
This part is already wrong (it is the factorisation of x^2 + x - 2, which is not the question)
I think this is what people have been trying to say?

Ohhhhhhhhhhh holy crap I get it.

Wow I'm already failing this test (legit) and i'm only one question in LOL

 

[HSC2014]

Re: 2012 Year 9 &10 Mathematics Marathon

Well it's already in the ax + bx + c form so why would we need to complete the square to find the minimum lmao

x^2 -8x +25
(x-4)^2 + 9
Therefore 4 is the axis of symmetry. Then you sub in x = 4 and you get the vertex to be (4,9).

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

Wait did I do question f correct?

m^4 - 5m^2 + 4 = 0

m^4 - 5m^2 = -4

m^2 (m^2 - 5) = -4

m^2 = -4 (no solution)

m^2 - 5 = -4

and then solve for m?

failing this hard

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

x^2 -8x +25
(x-4)^2 + 9
Therefore 4 is the axis of symmetry. Then you sub in x = 4 and you get the vertex to be (4,9).

oh my god

i can't even

 

[twinklegal19]

Re: 2012 Year 9 &10 Mathematics Marathon

Wait did I do question f correct?

m^4 - 5m^2 + 4 = 0

m^4 - 5m^2 = -4

m^2 (m^2 - 5) = -4

m^2 = -4 (no solution)

m^2 - 5 = -4

and then solve for m?

failing this hard

you can only do those steps if the RHS is 0

hint: let u=m^2 and reduce the quartic into a quadratic you already know

 

[ganji]

Re: 2012 Year 9 &10 Mathematics Marathon

IMO this test is a good indicator which areas you lack practice in

 

[kazemagic]

Re: 2012 Year 9 &10 Mathematics Marathon

Wait did I do question f correct?

m^4 - 5m^2 + 4 = 0

m^4 - 5m^2 = -4

m^2 (m^2 - 5) = -4

m^2 = -4 (no solution)

m^2 - 5 = -4

and then solve for m?

failing this hard

let k = m^2
so the equation is like k^2 - 5k +4 = 0
once u find k, u just sub into k = m^2 equation above

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

-_-

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

wait so is the answer for that plusminus 2 and 1?

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

Finally on question 1 g :')

 

[HSC2014]

Re: 2012 Year 9 &10 Mathematics Marathon

Mhm and this thread has been taken over by Demento's test lol..

 

[Demento1]

Re: 2012 Year 9 &10 Mathematics Marathon

IMO this test is a good indicator which areas you lack practice in

If only I remembered to add statistics.

Edit: In addition, I reckon 1hr 5 mins was slightly generous. I reckon it could be done properly in about 50 minutes.

 

[Fawun]

Re: 2012 Year 9 &10 Mathematics Marathon

Is it okay if I just sketch 2/x randomly and label it as 2/x because it has no intercepts and stuff so it doesn't matter? (lol)

that's what i've been doing so far hahaha

 

[Demento1]

Re: 2012 Year 9 &10 Mathematics Marathon

Is it okay if I just sketch 2/x randomly and label it as 2/x because it has no intercepts and stuff so it doesn't matter? (lol)

that's what i've been doing so far hahaha

My solutions will say otherwise. ^