checking maths answers

[mollykins]

Factor, and anyone else good at maths, i've done some stuff but can you check them please, I would get my mum or dad or friend to but; i lost mum and dad with most my work in year 9 and my friends are only doing foundation.

1) these are eqations of lines; (P) y=3x+5 (Q) y=4-3x (R) y+3x=1

a) which is parallel to y=3x ? P and Q

b) which goes through the point (2,7) ? S

c) write down the gradient of y+2x=7 ? +7 (is it necessary to say + ?)


And this at the start of a paper but i always find explaining things hard.

2) mike says that 18% or £840 is equal to 36% of £420

explain why he is correct, do not calculate 18% of £840.

18% is half of 36%. and 840 is double 420.

2 (n/2) = n ?????????? i have no idea if that is right.

3)make t the subject of the formula w=2t+v

-v . . . . . w-v=2t
1/2 . . . . (w-v)/2=t

when doing stuff liek that above, i normally draw a vertical line and and jot down my stages, similar to what i've done there, is that a good idea? When checking back over, its easier to spot mistakes i think and its clear to the examiner what i was doing.

[4getmenot]

you lost me at equation

[factor-fiction]

Good luck.
So what maths papers have you taken already if these are worth only 55% of teh total mark?
I thought modules 1&3 were done earlier and then Mod 5 in June

[mollykins]

i did mod 1 in november 2008 and 3 in june 2009

[jake-the-peg]

Dont forget to go from the gradient of 1 line to the gradient of the perpendicular it's the negative reciprocal

so y=3X+2 is perpendiculalr to y= -1/3 x +5 say

[factor-fiction]

That's what I'd have expected, but a bit earlier you said you had modules 3 and 5 this week.
Is it just Module 5, two papers (calculator and noncalculator)? i think they are only 75 minutes each.
(In my day GCSE(O level) papers were 2½ hours and A level papers were 3 hours)

[factor-fiction]

yes you're right jake-the-peg.
In my haste to answer before anyone else I slipped in an incorrect statement that two of the lines lines were perpendicular not parallel. I should have said they were simply not parallel..

[mollykins]

i'm confused, i'd have already done module 3 wouldn't i? i jsut looked and on my timetable it just says mod5, 75 minutes.

[mollykins]

oh and i thought this was really easy for an a grade question so might have misunderstood it.

simplify (x^2-4x+4)/(x^2-4) and i got -x+4

[factor-fiction]

I think you're wrong.
Doing it in my head I get (x-2)/(x+2)

[mollykins]

ummm, i cancelled out the x^2 s then i weren't entirely sure because -4 x 4 is -1 then you're elft with the minus 4x.

[factor-fiction]

Try again.

The top bit x²-4x +4 needs to be factorised into two brackets. You do it- i won't tell you theanswer yet.

Then factorise the bottom bit x²-4. (Difference of two squares).

Then put one over the other and cancel out common terms (a common pair of brackets)

[mollykins]

(x-2) (x-2) ? as the bttom one would have to half a plsu and minus
(x+2) (x-2)

[factor-fiction]

you can't just cancel out individual terms.

For example what is (8+4)/(4+2) = 12/6 =2. Agreed?
But you can't just cancel the 4s for example because your expression would become 8/2=4 which is the wrong answer.
You can only divide top and bottom by a common FACTOR
In your question the common factor is x-2

Sadly it is common for pupils who get grade A in maths to be able to unable to factorise and simplify expressions like this, and this will lead to problems when they do A level maths/science, so have another look and make sure you can do it.

[factor-fiction]

Sorry mollykins, my last post crossed with your latest one.
Your latest one is right if you've got (x-2)(x-2)/(x+2)(x-2) which simplifies to (x-2)/(x+2)

[mollykins]

aahhh, i thought it was to easy to be true.

[factor-fiction]

You've got it now, I think. Just remember that on questions like this you need to factorise the top and bottom then divide top and bottom by a common factor (a pair of brackets)

[north star]

As an aside, just wanted to wish you success in your exams next week (?) It's good to see someone with an apparent enthusiasm for the subject.

[mollykins]

Yeah thanks, my maths along with four other exam are next week, then four the week after that then two weeks with only one exam each.