Finding subject of a simple formula: solving y =7 - 2x for x

[nasher]

Hi all. I'm freshing my memory as I'm returning back to studying, working through various topics. I've stumbled across this issue I cannot get my head around.

I've got the following formula: y =7 - 2x and I'm trying to find x. Now all I remember is that what you do on one side you do to the other. Are there any special cases where if you have a co efficient on the left of the subject? I have the answer to the above and it's:

X = 7-y / 2

I would of thought it'll be

X = y + 7 / 2

What pitfalls am I missing? Thanks

 

[stapel]

To refresh on how to solve linear and then literal equations, please try here and then here.

I've got the following formula: y =7 - 2x and I'm trying to find x. Now all I remember is that what you do on one side you do to the other. Are there any special cases where if you have a co efficient on the left of the subject?

I'm not sure what you mean by this question...?

I have the answer to the above and it's:

X = 7-y / 2

I will guess that you mean "X" to actually be "x". (They're not the same variable, obviously.) I'm not sure, by the right-hand side of what you've posted, whether you mean:

. . . . .\(\displaystyle \mbox{a. }\, x\, =\, 7\, -\, \dfrac{y}{2}\)

...or:

. . . . .\(\displaystyle \mbox{b. }\, x\, =\, \dfrac{7\, -\, y}{2}\)

By the way, (b) is the correct solution.

I would of thought it'll be

X = y + 7 / 2

What pitfalls am I missing?

Since you haven't posted your work, there is no way for us to check into which "pits" you may have "fallen". Kindly please reply with that information. Thank you!

 

[Harry_the_cat]

Hi all. I'm freshing my memory as I'm returning back to studying, working through various topics. I've stumbled across this issue I cannot get my head around.

I've got the following formula: y =7 - 2x and I'm trying to find x. Now all I remember is that what you do on one side you do to the other. Are there any special cases where if you have a co efficient on the left of the subject? I have the answer to the above and it's:

X = 7-y / 2

I would of thought it'll be

X = y + 7 / 2

What pitfalls am I missing? Thanks

Think of the two sides of the equation as a set of scales. At the start they are balanced, so if you do something to one side, you have to do the same to the other side to keep them balanced.

I'm guessing (seeing you haven't shown us) that you are attempting to add 7 to both sides of y = 7 - 2x.

But this would give you y + 7 = 14 - 2x NOT y + 7 = 2x (which, again I'm guessing, is where you got your final (incorrect) answer from.)