haydon_peter Posted April 2, 2011 Report Share Posted April 2, 2011 When my teacher went over it (wasnt listening, dont remember what i was doing) he turned it into an equation somehowThat's your problem right there. Quote Link to comment Share on other sites More sharing options...
Kieran Morrison Posted April 2, 2011 Author Report Share Posted April 2, 2011 I was taught both BODMAS and BOMDAS. I'm also a user of Nofclbrih... it's a good word which is worth remembering in Chemistry. Bomdas, Bodmas, Bidmas and pedmas (the american one!) Quote Link to comment Share on other sites More sharing options...
Kieran Morrison Posted April 2, 2011 Author Report Share Posted April 2, 2011 So, This is the kind of question we got in the last test: 9x-4 = 63 Now, is the following right? 1) 9x-4=63 +4 = 9x = 63 63 / 9 = 7 x=7 Do you add with every equation that has -'s in it? See in an equation like this : 4x-9 = 7x + 5 do you add the x's? How does it work? Could somebody solve it for me and show me the working so i know what to do? Thanks alot Kieran Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted April 2, 2011 Report Share Posted April 2, 2011 So, This is the kind of question we got in the last test: 9x-4 = 63 Now, is the following right? 1) 9x-4=63 +4 = 9x = 63 63 / 9 = 7 x=7 No, if you follow it you've added 4 to the left hand side to remove it but you haven't added 4 to the right hand side. What you should have is: 9x - 4 = 63 9x - 4 + 4 = 63 + 4 9x = 67 x = 67/9 x= 7.444... Do you add with every equation that has -'s in it? See in an equation like this : 4x-9 = 7x + 5 do you add the x's? Not sure what you mean by adding the x's. You don't necessarily do anything to every equation, it all depends on what you have to begin with. In the equation you give: 4x - 9 = 7x + 5 Get all the x terms on the left and all the numbers on the right. To do that we subtract 7x from both sides and add 9 to both sides: 4x (- 7x) - 9 (+ 9) = 7x (- 7x) + 5 (+ 9) A bit too much going on there but you should then get: -3x = 14 We can now divide both sides by -3 to get x on its own on the left: -3x/-3 = 14/-3 x = -4.666... The key to it all is that you have to rearrange the equations to be left with x on the left. To do this you carry out operations but if you do anything to one side you MUST do it to the other. If one side needs 3 subtracted to get rid of what's there to start with you MUST subtract three from the other side of the equals sign to make sure everything remains balanced and correct. If you consider it in just numbers, you know that 5 + 3 = 8. If we subtract 3 from the left and nothing else you end up with 5 = 8. Which is clearly wrong. However if we subtract 3 from BOTH sides, in exactly the same way as you do in an equation containing unknowns like x, you would get 5 = 8-3 = 5 which is correct. 1 Quote Link to comment Share on other sites More sharing options...
Simpson Posted April 2, 2011 Report Share Posted April 2, 2011 Yea Dave. You might just wanna go and speak to your teacher, you really don't seem to be understanding the method at all. Quote Link to comment Share on other sites More sharing options...
Kieran Morrison Posted April 2, 2011 Author Report Share Posted April 2, 2011 No, if you follow it you've added 4 to the left hand side to remove it but you haven't added 4 to the right hand side. What you should have is: 9x - 4 = 63 9x - 4 + 4 = 63 + 4 9x = 67 x = 67/9 x= 7.444... Not sure what you mean by adding the x's. You don't necessarily do anything to every equation, it all depends on what you have to begin with. In the equation you give: 4x - 9 = 7x + 5 Get all the x terms on the left and all the numbers on the right. To do that we subtract 7x from both sides and add 9 to both sides: 4x (- 7x) - 9 (+ 9) = 7x (- 7x) + 5 (+ 9) A bit too much going on there but you should then get: -3x = 14 We can now divide both sides by -3 to get x on its own on the left: -3x/-3 = 14/-3 x = -4.666... So, with equations like that with 1 or 2 -'s, you add the numbers? And would you not be minusing the 4x from 7 because its smaller? And i would talk to my teacher but the test is on monday and i dont know the questions so doing some revision lol Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted April 2, 2011 Report Share Posted April 2, 2011 So long as you always do the same to both sides of the equals sign you'll be fine. You want to end up with your variable (x/y/whatever) on one side and just numbers on the other. The rest is up to you. Practice practice practice. Quote Link to comment Share on other sites More sharing options...
JT! Posted April 2, 2011 Report Share Posted April 2, 2011 So, with equations like that with 1 or 2 -'s, you add the numbers? And would you not be minusing the 4x from 7 because its smaller? And i would talk to my teacher but the test is on monday and i dont know the questions so doing some revision lol You seem to have a fundemental misunderstanding of negative numbers which really isn't helping. In the example you gave: 9x - 4 = 63 It can be written like this -4 + 9x = 63 They're exactly the same thing. And in either example you would add 4 to both sides of either equation. The general rule is, if there's a negative number in there (x-4), you more than likely have to add to both sides, if there's a positive (x+4) number in there, you'll have to subtract from both sides. Really, all these are are basic number puzzles. You keep eliminating as much as you can until you can't go any further, and that's the answer. Quote Link to comment Share on other sites More sharing options...
Kieran Morrison Posted April 3, 2011 Author Report Share Posted April 3, 2011 (edited) I You seem to have a fundemental misunderstanding of negative numbers which really isn't helping. In the example you gave: 9x - 4 = 63 It can be written like this -4 + 9x = 63 They're exactly the same thing. And in either example you would add 4 to both sides of either equation. The general rule is, if there's a negative number in there (x-4), you more than likely have to add to both sides, if there's a positive (x+4) number in there, you'll have to subtract from both sides. Really, all these are are basic number puzzles. You keep eliminating as much as you can until you can't go any further, and that's the answer. Oh God. I. get it now, its a negative so you must add or it will go on forever. I get it now, cheers everyone:) Edited April 3, 2011 by Kieran Morrison Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted April 3, 2011 Report Share Posted April 3, 2011 Oh God. I. get it now, its a negative so you must add or it will go on forever. I get it now, cheers everyone:) I swear that was mentioned on the first page of this thread and many times subsequently! In the example you gave: 9x - 4 = 63 It can be written like this -4 + 9x = 63 They're exactly the same thing. Following from that (and to take what Luke said and also the way you're looking at it), So long as you do the same to both sides it'll aaaallll be goooood. It's not about what's smallest or biggest (that just makes your life easier) but you can do it any way you like: 9x - 4 = 63 For shits and giggles subtract 63 from both sides and subtract 9x from both sides gives: -67 = -9x Divide both sides by -9: -67/-9 = x x = 7.444... So long as you've carried out the same operations on both sides it'll work out, you just may need to deal with the odd negative in there. Quote Link to comment Share on other sites More sharing options...
Kieran Morrison Posted April 3, 2011 Author Report Share Posted April 3, 2011 I'm revising on that MyMaths website and i came across this... 7-5x=5x+10 (add 5 x to both sides) 7=10x + 10 (take 10 from both sides) The take ten is what confused me. Why do you change from adding, to taking away? is it because there is only a plus lef and there is no minus sign anymore so you would minus? Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted April 3, 2011 Report Share Posted April 3, 2011 I'm revising on that MyMaths website and i came across this... 7-5x=5x+10 (add 5 x to both sides) 7=10x + 10 (take 10 from both sides) The take ten is what confused me. Why do you change from adding, to taking away? is it because there is only a plus lef and there is no minus sign anymore so you would minus? It has nothing to do with what you've done before and only to do with what you need to do in order to rearrange the equation to get all the x's on one side and all the numbers on the other. You're correct- you add 5x to both sides which means all the x's are on the right. You now want all the numbers on one side (for ease get them on the left) so as you say you want to subtract 10 from both sides. There are other ways you could do it but the shortest route is what you've said. Don't think about what you've done before though- that's largely irrelevant. Only consider what's left and what you have to do to get all the x's on one side (so you can eventually solve for a single x) and all the numbers n the other side, remembering to do the same to both sides each time. Edit: An example picked out of thin air to try and show it.. 5x - 3x -10 + 4 = 4x - 12 You probably won't see anything like that because you'll be given problems which have already been simplified but starting there, collect like terms first: 2x - 6 = 4x - 12 I'm going to collect the x's on the left so first I'll subtract 4x from both sides: -2x - 6 = -12 Now collect the numbers on the right by adding 6 to both sides (that will remove the -6 on the left): -2x = -6 So now we just divide both sides by -2 (to get x on its own on the left): x = 3 You can double check if that's correct by substituting x = 3 back into any of the equations above. Just to prove it stick x = 3 back into the original equation: 5x - 3x -10 + 4 = 4x - 12 5(3) - 3(3) - 10 + 4 = 4(3) - 12 15 - 9 - 10 + 4 = 12 - 12 0 = 0 Which is lucky. But proves the answer is correct (i.e. the equation is true). Quote Link to comment Share on other sites More sharing options...
JT! Posted April 3, 2011 Report Share Posted April 3, 2011 I'm revising on that MyMaths website and i came across this... 7-5x=5x+10 (add 5 x to both sides) 7=10x + 10 (take 10 from both sides) The take ten is what confused me. Why do you change from adding, to taking away? is it because there is only a plus lef and there is no minus sign anymore so you would minus? All you're doing with these equations is to make as many "0" or "0x" as possible. Every step that is you're goal. If there's a -5x you have to add 5x to make it 0x, once you have a 0x, or a 0 you can just get rid of it. There's a +10, so you need to minus 10 to make it 0. Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted April 3, 2011 Report Share Posted April 3, 2011 It's also worth pointing out that so long as you do the same to both sides, the equation remains correct and you can't really go wrong. Taking the example you give again, 7 - 5x = 5x + 10, rather than adding 5x to both sides, subtract 5x from both sides. That gives: 7 - 10x = 10 Now instead of subtracting 10 from both sides, subtract 7 instead: -10x = 3 You should find that doing it that way will give you exactly the same answer for x as the way you say, it might take a different number of steps but because you've done the same operations to both sides of the equation it will still be true and therefore correct. Quote Link to comment Share on other sites More sharing options...
JD™ Posted April 3, 2011 Report Share Posted April 3, 2011 Just as another way of wording it, because it seems you might need it explained in a few different ways to choose which one flicks the switch for you (and in a non patronising way, we've all been there). Each time you've changed the equation, treat the new one exactly as if it was a brand new equation you were seeing for the first time. What you've done before (as long as you've done it right) won't matter. DEFINITELY don't forget that you get most of your marks for working, so if you end up with the wrong answer you'll still get marks if you do the working. Quote Link to comment Share on other sites More sharing options...
Tomm Posted April 3, 2011 Report Share Posted April 3, 2011 This thread is simultaneously hilarious, infuriating, brilliant and concerning. Keiran, go and speak to a teacher or someone who understands maths, like a relative. I don't think the forum is the best place to try and learn maths, it's pretty confusing the way everyone is writing things (it's hard to write equations on a PC). This isn't as hard as you're making it out to be - you just need to go through it with someone and everything with fall into place. Alternatively, keep going and I'll grab some popcorn. Quote Link to comment Share on other sites More sharing options...
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