Subracting Equations

[monkeyseemonkeydo]

So if there is 9x+21=5x-4, you would minus 5x from each side, then minus 4 of each giving you 4x = 17 then divide them both by 4 giving you the answer- X = 14.25?

As an alternative to what Jason wrote, and in line with the direction you're going for:

9x+ 21 = 5x -4

Subtract 5x from both sides:

4x + 21 = -4

Add 4 to each side (if you subtract 4 from each side you wouldn't be helping to simplify the problem):

4x + 25 = 0

This can then be rearranged by subtracting 25 from each side:

4x = -25

Which gets you back to x = -6.25.

Edit: Also, how did you manage to end up with 14.25 when you divide 17 by 4?!

[Kieran Morrison]

Edit: Also, how did you manage to end up with 14.25 when you divide 17 by 4?!

My calculator did it! I must have typed it wrong or something.

So am i right though in saying if there is 2 minus's in an equation, it means you add them, the same with 2 + signs, and if there is a minus and a plus you minus them?

[monkeyseemonkeydo]

So am i right though in saying if there is 2 minus's in an equation, it means you add them, the same with 2 + signs, and if there is a minus and a plus you minus them?

Pretty sure the answer is no... The only time when two minus signs make a positive is when you have the two signs together.

For example 4 - 1 = 3. But if you have 4 - (-1) ( read as four subtract minus one) then the two minuses combine to become an addition.

So 4 - (-1) = 4 + 1 = 5

Going back to equations lets make everything negative to show how it works.

Start with -4x - 6 = -14

We want all the x's on one side and all the numbers on the other so to get rid of the -6 on the left we add 6 to both sides:

-4x - 6 + 6 = -14 + 6

-4x = -8

We can now find x by dividing both sides by -4, to leave just one positive x on the left:

-4x/-4 = -8/-4

x = 2

Does that make sense?

[Matt Vandart]

Apples and Bannanas.

[Kieran Morrison]

Still not sure on how to do equations like: if x is 9, and y is 10 whats xy²

When my teacher went over it (wasnt listening, dont remember what i was doing) he turned it into an equation somehow, like the kind of equations written like: 5x + 3 = 9x + 21 and i dont know how he did it

So how would you turn the x is 9, and y is 10 whats xy²into an equation like above?

[monkeyseemonkeydo]

So how would you turn the x is 9, and y is 10 whats xy²into an equation like above?

The type you describe are some of the easiest you can come across as you're basically given the answer. All you need to do is substitute the numbers given (x=9, y=10) into the formula given (xy²). The only thing you need to remember is what to square. In this case if you were to write the formula out slightly differently you'd have

x * y²

Noting that only the y term is being squared.

Substituting x=9 and y=10 gives:

9 * 10²

Which becomes:

9 * 100

Which = 900.

Edit: Not entirely sure how your teacher will have turned it into a proper equation without introducing another unknown (lets say z).

In this case we can write z = xy²

Because we know x and y we have one equation and one unknown (z) which means we can solve it.

So following what we did before:

z = 9 * 10²

z = 900.

You can always check these things by going backwards. If we pretend we don't know what y is we can start with the same equation as before:

xy² = z

So if we first rearrange for y:

y² = z/x

y = squareroot(z/x)

And now substituting z = 900 and x = 9 into that we get:

y = squareroot(900/9)

y = squareroot(100)

y = 10

Is that taking it too far?

[Kieran Morrison]

Is that taking it too far?

Yes, my teacher managed to turn it into a simple equation, that was soooo confusing lol

[JT!]

Still not sure on how to do equations like: if x is 9, and y is 10 whats xy²

When my teacher went over it (wasnt listening, dont remember what i was doing) he turned it into an equation somehow, like the kind of equations written like: 5x + 3 = 9x + 21 and i dont know how he did it

So how would you turn the x is 9, and y is 10 whats xy²into an equation like above?

Well, it already is an equation.

xy² you can turn into x*y*y or xyy but that's pretty much about it.

If you had to solve it, it's simply 9*10² which is 900.

There's not really much more that can be done with it.

[Kieran Morrison]

Well, it already is an equation.

xy² you can turn into x*y*y or xyy but that's pretty much about it.

If you had to solve it, it's simply 9*10² which is 900.

There's not really much more that can be done with it.

Why would it be 2 y's?

[monkeyseemonkeydo]

Why would it be 2 y's?

Because it's y² which is y * y.

3² = 3 * 3 = 9.

[Kieran Morrison]

Because it's y² which is y * y.

3² = 3 * 3 = 9.

No, it's squaring both the x and the y.

Well thats how we did it in school.

[monkeyseemonkeydo]

No, it's squaring both the x and the y.

No, it isn't. Trust me. Did you actually read my post? If you have xy², ONLY the y is being squared. As JT says, that means it can be rewritten as x * y * y. It's really not difficult...

[Kieran Morrison]

No, it isn't. Trust me. Did you actually read my post? If you have xy², ONLY the y is being squared. As JT says, that means it can be rewritten as x * y * y. It's really not difficult...

So, could it be re-written as 9x + 81 = 10x + 100?

So would you get x squared, then y squared, then square the number you get?

I dont understand this

[dirt jumper jake]

Its xy2 (dont know how to make a sqaured number on a comp ) if it was to give you two x's and two y's, it would be x2y2, you get me?

[monkeyseemonkeydo]

So, could it be re-written as 9x + 81 = 10x + 100?

So would you get x squared, then y squared, then square the number you get?

Where did you get that equation from? Work it through:

9x + 81 = 10x + 100

x = -19

Which obviously isn't right and you've lost the y's...

9x + 81 = 10y +100

Substituting for x and y gives:

81 + 81 = 100 + 100

162 = 200

Which also obviously isn't right.

[Kieran Morrison]

Its xy2 (dont know how to make a sqaured number on a comp ) if it was to give you two x's and two y's, it would be x2y2, you get me?

Yeah

[monkeyseemonkeydo]

if it was to give you two x's and two y's, it would be x²y², you get me?

Which can also be written as (xy)².

[dirt jumper jake]

Which can also be written as (xy)².

Yeah, how do you do the little 2's then?

[monkeyseemonkeydo]

Yeah, how do you do the little 2's then?

When you write a post there are the A₂ and A² buttons to make subscript and superscripts next to all the bold, italic etc. buttons .

[dirt jumper jake]

When you write a post there are the A₂ and A² buttons to make subscript and superscripts next to all the bold, italic etc. buttons .

Never noticed that, cheers

[JT!]

No, it's squaring both the x and the y.

Well thats how we did it in school.

"BODMAS"

Brackets, orders (squared/cubed), division, multiplication addition subtraction.

That's the order of operations. Orders take priority over everything else other than brackets.

[Revolver]

"BODMAS"

Brackets, orders (squared/cubed), division, multiplication addition subtraction.

That's the order of operations. Orders take priority over everything else other than brackets.

BIDMAS, you mean.

I for indeces!

Edited April 1, 2011 by Revolver

[JT!]

I got taught bodmas, but I thought the O was for powers of.

[DrDoom]

http://jforjustice.co.uk/banksters

[monkeyseemonkeydo]

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.