# make x the subject

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#1
y=x-5 rearrange the formulae to make x the subject
0
4 years ago
#2
x=y+5
1
4 years ago
#3
(Original post by Harryacko)
y=x-5 rearrange the formulae to make x the subject
Are you a troll??? Even my 4 year old cousin brother can do this!!!
Well it's x=y+5
5
4 years ago
#4
The topic for this is "rearranging forumulae", this is fairly simple.
0
4 years ago
#5
(Original post by Harryacko)
y=x-5 rearrange the formulae to make x the subject
"To make x the subject" means to have an equation with all the terms in x on one side.Currently, y is the subject of the equation.

To make x the subject, you need to 'move' the -5 from the right hand side of the equation onto the left hand side.

We do this by adding 5 to both sides. This is because -5 + 5 = 0 and so we will simply be left with: y + 5 = x + 0 which is the same as y+5 = x. This is the right answer, but we usually prefer to write it as x = y+5.

Now try making x the subject of the following:

(1) y = x + 2

(2) y = 2 - x

(3) 2y + 3 = 2x -1
2
1 year ago
#6
X/a(squared) 3b = 2c Make x the subject
0
1 year ago
#7
I need help with it for my homework I don’t understand
0
1 year ago
#8
(Original post by Hello hshsb)
X/a(squared) 3b = 2c Make x the subject
x = (2a^2 * c) / 3b

sorry I can't quite explain what I did as I just did it in my head but it's about dividing anything on the left of the = to get X on it's own
0
1 year ago
#9
X/3bA^2 = 2c... The question, just rearranged so it's simpler to think out.

Now we have to make X, the subject

If something is divided by another thing and you wish to make the whatever is on the top the subject, in this case X. You simply multiply the bottom to each side of the question.

X =(A^2) (3B) (2C)
=6A^2BC
0
1 year ago
#10
0
1 year ago
#11
(Original post by Filipina.x)
xy-x=0
x(y-1)=0
x=0

right?

shoreyr015
Unless y = 1 as then x = x
1
1 year ago
#12
XY=X+A
why is this confusing me? help!
0
1 year ago
#13
(Original post by shoreyr015)
XY=X+A
why is this confusing me? help!
Take your x’s to one side
xy-x=a

Factorise
x(y-1)=a

Bring y-1 to the other side through division
x=a/y-1
Last edited by Filipina.x; 1 year ago
0
1 year ago
#14
(Original post by Filipina.x)
Take your x’s to one side
xy-x=a

Factorise
x(y-1)=a

Bring y-1 to the other side through division
x=a/y-1
Thank you! That makes so much sense no idea why I was so confused
0
1 year ago
#15
0
1 year ago
#16
(Original post by Harryacko)
y=x-5 rearrange the formulae to make x the subject
x=y+5
0
9 months ago
#17
??
0
9 months ago
#18
(Original post by papie)
??
This was a while ago, don’t worry about it
0
9 months ago
#19
y=x-5 rearrange the formulae to make x the subject

That's how you do it.
-multiply both sides by 2
2y=2x-10
-now take square roots of both sides

Sqrt(2y) = sqrt(2x) - sqrt(10)
-rewrite everything in terms of powers
2y^(1/2) = 2x^(1/2) - 10^(1/2)

Now the problem is you've got powers to deal with so best thing here is to take logs of both sides.
SO,
log 2y^(1/2) = log 2x^(1/2) - log 10^(1/2)

now you can use the logarithmic power rule logb(x y) = y ∙ logb(x)
So this becomes: 1/2 * log 2y = 1/2 * log 2x -1/2 * log 10
let's rearrange and factorize:
1/2 * log 2y - 1/2 * log 2x = -1/2 log 10

1/2 (log 2y - log 2x)= -1/2 log 10 Divide both sides by 1/2

log(2y -2x) = -1

now you have to find a way to remove logs from both sides otherwise we can not change subject right? so because we need same base which is log, so they cancel out !
you have to rewrite -1 as logs so we have logs on both sides. i didn't write before but all logs here were base 10
so -1 in log 10 base is log (10) (10^-1)
so this becomes
Log(10)(2y-2x) = -1 log (10)
Use logarithmic power rule again to bring -1 as power

Log (10)(2y-2x)= log(10)^1
now logs cancel out and you're left with

2y -2x = 10
You can not make x subject till x is not alone in one side so lets first rearrange:
2x = 2y -10
and now divide both sides by 2.
x = 5 - y
It's actually quite simple but you need to remember logs and their properties.
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