Current Year 11 thread mark III (woo!) / Year 12 2012/13

Original post by meeow

set 4x-y=17 as 4(5+y)-y =17 :smile:

It works! Thank you very much kind lady.

I was unaware that I had to retain the -y after (5+y). Anyone care to explain?

(edited 11 years ago)

Reply 4603

Melissajanex

Original post by InvertedLayman

Hello ladies and chaps, anyone care to help me with these simultaneous equations?:

4x-y=17 and x=5+y

I think I have to use substitution but I don't really know what I'm doing.

I would re-arrange it so that it's x-y=5. Then take them away so you get 3x=12 which means x=4. You can then substitute it in to get y which is -1. Hope this helps

Reply 4604

Adriennet

Original post by InvertedLayman

Hello ladies and chaps, anyone care to help me with these simultaneous equations?:

4x-y=17 and x=5+y

I think I have to use substitution but I don't really know what I'm doing.

4x=17-y and
x=5+y
4x= 17-y
4x=20+y
8x=37
X=37/8
Then sub in original equation to get y. I think!

Reply 4605

Original post by InvertedLayman

Hello ladies and chaps, anyone care to help me with these simultaneous equations?:

4x-y=17 and x=5+y

I think I have to use substitution but I don't really know what I'm doing.

4(5+y)-y=17
20+4y-y=17
3y=-3
y=-1

x=5+(-1)
x=4

;D

Reply 4606

Pandora.

Original post by multiplexing-gamer

Yeah you need a career what an American couldn't offer. It's annoying as it's really difficult for us Brits to live in cool places but everyone else comes to our country.

Or marry an American... :colone:

I know what you mean. :frown:

Still, I don't mean this in a big headed way but most of us on TSR are people who go to university/planning to go to university, so I guess we're in the best position possible to get that kind of career. :smile:

I struggle to think of anything that I'd be interested in that would constitute a career that most Americans could offer though. :frown:

Reply 4607

Why in this question:
6x+y=9 (1)
y=3x-9 (2)

Was the +y in (1) not retained, making 6x+(3x=9)=9?

Reply 4608

Original post by InvertedLayman

It works! Thank you very much kind lady.

I was unaware that I had to retain the -y after (5+y). Anyone care to explain?

The (5+y) is only the value of x, so you have to keep the rest of the equation for it to work. That probably didn't make sense. ;D
Basically, they're telling you that x= 5+y, so you're using that as a value of x. Like for example, say somebody told you that the value of x was 2, and you had to put it into an equation as follows;
y= 5x+6
You'd do, 5(2) but you'd also have to add the +6 afterwards so you get the full value of y. ;D
Don't worry, I've confused myself haha.

Reply 4609

Alexx53

Original post by InvertedLayman

Why in this question:
6x+y=9 (1)
y=3x-9 (2)

Was the +y in (1) not retained, making 6x+(3x=9)=9?

Because in this example you are substituting out the 'y' for y=3x-9. In the previous example you substituted out the 'x', which meant the y stayed. (This time the '6x' is staying and the 'y' is being replaced).

Reply 4610

Original post by Deziah

The (5+y) is only the value of x, so you have to keep the rest of the equation for it to work. That probably didn't make sense. ;D
Basically, they're telling you that x= 5+y, so you're using that as a value of x. Like for example, say somebody told you that the value of x was 2, and you had to put it into an equation as follows;
y= 5x+6
You'd do, 5(2) but you'd also have to add the +6 afterwards so you get the full value of y. ;D
Don't worry, I've confused myself haha.

Niiice all right I get it.. I think.

Reply 4611

Original post by Alexx53

Because in this example you are substituting out the 'y' for y=3x-9. In the previous example you substituted out the 'x', which meant the y stayed. (This time the '6x' is staying and the 'y' is being replaced).

Oh right because in this one they tell you the equation for y so you don't need the letter y there any more, should have seen that.

Reply 4612

lil-mazie

I'm really struggling to get into the 'revision mood' I have a maths test on the 11th and I haven't really revised I'm aiming for a B or higher but I find it so difficult to revise. I woke up at 10 and left the house at 11 I have been in the library till 3;00 i left making all these excuses like I'm going to do work at home but it seems like it won't happen. I don't want to get lazy but I feel like going to sleep and starting off properly tomorrow
What do I do????

This was posted from The Student Room's iPhone/iPad App

Reply 4613

Original post by InvertedLayman

Niiice all right I get it.. I think.

It's basically like saying;
y = 3 + 4
y = 3 + (2x2)
If you've subbed in the value of 4 as 2x2, then you don't need the +4 any more, otherwise it would be y = 3 + 4 + (2x2) which would change the value of y. It's just another way of saying numbers, confusing I know. ;D

Reply 4614

Original post by lil-mazie

I'm really struggling to get into the 'revision mood' I have a maths test on the 11th and I haven't really revised I'm aiming for a B or higher but I find it so difficult to revise. I woke up at 10 and left the house at 11 I have been in the library till 3;00 i left making all these excuses like I'm going to do work at home but it seems like it won't happen. I don't want to get lazy but I feel like going to sleep and starting off properly tomorrow
What do I do????

This was posted from The Student Room's iPhone/iPad App

The trick is, to stay away from all electronic devices and stick to a good book. And make a plan on how many topics you will cover each day.

Reply 4615

Alexx53

Original post by lil-mazie

I'm really struggling to get into the 'revision mood' I have a maths test on the 11th and I haven't really revised I'm aiming for a B or higher but I find it so difficult to revise. I woke up at 10 and left the house at 11 I have been in the library till 3;00 i left making all these excuses like I'm going to do work at home but it seems like it won't happen. I don't want to get lazy but I feel like going to sleep and starting off properly tomorrow
What do I do????

This was posted from The Student Room's iPhone/iPad App

I haven't done any revision since Friday either. I keep telling myself the exams are ages away and I have loads of time to revise later in the week.

You could always go to McDonalds or somewhere like that and tell yourself if you don't revise you'll end up working there :tongue:

Or some sort of reward system if you do a certain amount of work? Or unplug/remove all distractions so you're forced to revise.

Reply 4616

Original post by Deziah

It's basically like saying;
y = 3 + 4
y = 3 + (2x2)
If you've subbed in the value of 4 as 2x2, then you don't need the +4 any more, otherwise it would be y = 3 + 4 + (2x2). It's just another way of saying numbers, confusing I know. ;D

Nope, it makes perfect sense, thanks again for your help. I don't know why but I find some "harder" questions in maths easier than the "easier" ones, because I miss out these obvious things.. sometimes.

Reply 4617