How do I rearrange this ?

hey guys I have a question

if I have 3x^2 -10x +7 = 0

how do I make x the subject and hence find x ?

first I made it : 3x^2 -10x = -7

but I don't know how to rearrange this algebraically

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Reply 1

Farhan.Hanif93

Original post by kingkongjaffa

hey guys I have a question

if I have 3x^2 -10x +7 = 0

how do I make x the subject and hence find x ?

first I made it : 3x^2 -10x = -7

but I don't know how to rearrange this algebraically

Quadratic formula or complete the square? (I suggest the former)

Are you aware of those techniques?

Reply 2

Tizmo

Basically, simply all that you can in the first step.

3x*2 - 10x +7 = 0 will become
6x -10x +7 = 0, which will become
-4x + 7 = 0, which will become
-4x = -7, so
x = -7/-4, the minuses cancel each other out, so basically,

x= 7/4

Is this the type of simplification that you mean? Or have I misunderstood the point?

Point taken, wrong type of math. :shiftyrun:

Sorry guys, please don't mind this post!

(edited 13 years ago)

Reply 3

birduk

(3x-7)(x-1)= 0...

Then carry on...

Reply 4

eliotball

Original post by Farhan.Hanif93

Quadratic formula or complete the square? (I suggest the former)

Are you aware of those techniques?

This

Original post by Tizmo

NOT this :O

Reply 5

kingkongjaffa

yes but I didn't think these would be necessary this is a differentiation question. Thanks.

Reply 6

birduk

Not what Tizmo said!

I'll carry on then...

if the above is true then x=1 or x=7/3

Reply 7

kingkongjaffa

Original post by Tizmo

you sir have misread the question that 3x is raised to the power of two not multiplied by 2

3x squared, not 3x*2 :smile:

Reply 8

Farhan.Hanif93

Original post by Tizmo

Firstly, please don't post full solutions, it's against the way we post help on here.

Secondly, make sure you understand what you're helping with before posted otherwise that could lead to further confusion.

Original post by birduk

(3x-7)(x-1)= 0...

Then carry on...

The question asks you to make x the subject first so factorising is not the way to go.

Reply 9

kingkongjaffa

Original post by birduk

Not what Tizmo said!

I'll carry on then...

if the above is true then x=1 or x=7/3

thanks how do you come to that? I'm not very good at factorising with things that have coefficients of x :P

Reply 10

eliotball

Original post by kingkongjaffa

thanks how do you come to that? I'm not very good at factorising with things that have coefficients of x :P

Use the quadratic formula then, it always works! :smile:

Reply 11

matthew769

is this for c2? i have a funny feeling i recognise this question and if so its in differentiation and you do have to factorise the quadratic

Reply 12

kingkongjaffa

No birduk is right by make the subject i didnt mean in that sense sorry for the confusion.

ya it is

Sorry guys, totally misread the question!

Please don't mind my post.

(edited 13 years ago)

Reply 15

eliotball

Original post by Tizmo

Sorry guys, totally misunderstood the question!

Please don't mind my post.

*misread

Reply 16

Tizmo

Original post by eliotball

*misread

What I meant to say. Cheers mate.

Reply 17

crazycake93

Original post by kingkongjaffa

hey guys I have a question

if I have 3x^2 -10x +7 = 0

how do I make x the subject and hence find x ?

first I made it : 3x^2 -10x = -7

but I don't know how to rearrange this algebraically

Factorise...

3x^2-10x +7 = 0

ac = 21

(3x^2 -3x) (-7x + 7)=0

3x(x-1) -7(x -1) = 0

(3x - 7) (x-1) =0

x = 7/3 and x = 1

Reply 18

eliotball

Original post by Tizmo

What I meant to say. Cheers mate.

No problem, I'm sure you had good intentions posting that solution, it was just a pretty awful mistake :P

Reply 19

kingkongjaffa

Original post by crazycake93

Factorise...

3x^2-10x +7 = 0

ac = 21

(3x^2 -3x) (-7x + 7)=0

3x(x-1) -7(x -1) = 0

(3x - 7) (x-1) =0

x = 7/3 and x = 1

ooh can you explain this please firstly AC is 3*7 but can you explain why you did that.
secondly can you explain how you go from 3x(x-1) -7(x-1) to (3x-7) (x-1)?