how to solve this quadratic? - Printable Version

how to solve this quadratic? - Printable Version

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how to solve this quadratic? - [EDT]AmanSingh123 - 04.10.2011

question is solve this equation:-

3x^2 = 6x

_______________________

and also it says to solve a quadratic quation you should put into this form, ax^2 + bx + c = 0

so i did:-

3x(x-2)=0

so i presumed that x would be 3 because 3x = 0 would be x = 3 to make x the subject

and then i did x-2 = 0 and then i got x = 2

so my answer was x = 3 or x = 2

but in the answer book it was x = 0 or x = 2

_______

i got two but im confused why its 0 and not 3?

Re: how to solve this quadratic? - Mark™ - 04.10.2011

Your answer book is correct. Its 0 and 2 both.

Re: how to solve this quadratic? - Hiddos - 04.10.2011

I think it's rather obvious:

Код:

3x^2 = 6x
x^2 - 2x = 0
x(x - 2) = 0

Now I think you've learned that this concludes that x = 0 v x = 2. For some proof, let's fill in those x's:

Код:

x(x - 2)

x = 0:

0 * (0 - 2)

If you multiply something with zero, it's zero.

Код:

x = 2

2 * (2 - 2) -> 2 * 0

Multiply with zero, stays zero.

If you fill in x = 3:

Код:

3 * (3 - 2) -> 3 * 1 = 3

Got it?

Re: how to solve this quadratic? - Vince - 04.10.2011

Quote:

Originally Posted by [EDT]AmanSingh123

because 3x = 0 would be x = 3

What? Essential mathematical fail. To get x out of that equation, you would divide both sides of it by 3; and 0/3 is still 0.

Re: how to solve this quadratic? - [EDT]AmanSingh123 - 04.10.2011

this is quadratics to be solved so the answer is always.... x = ? or x = ?

also i solved it out and saw where i went wrong

btw A-Level maths

Re: how to solve this quadratic? - RyDeR` - 04.10.2011

3xІ = 6x
<=> 3xІ - 6x = 0

D = bІ - 4.a.c = (-6)І - 4.3.0 = 36

(-b ± √D) / 2.a

<=> (6 ± 6) / 6

x1 = 2
x2 = 0

That was pretty easy.

EDIT: You already solved it. -.-

Re: how to solve this quadratic? - Mark™ - 04.10.2011

Its not A-level or B -level math, all u gotta know is the basics of equations, and then u can solve any kinda em', got it ?

Re: how to solve this quadratic? - CaHbKo - 04.10.2011

Ryder's right.

Btw you can check your answers (and do a lot more) there:
http://www.wolframalpha.com/input/?i=3x%5E2+%3D+6x

Re: how to solve this quadratic? - donB - 04.10.2011

Quote:

Originally Posted by [EDT]AmanSingh123

question is solve this equation:-

3x^2 = 6x

_______________________

and also it says to solve a quadratic quation you should put into this form, ax^2 + bx + c = 0

so i did:-

3x(x-2)=0

so i presumed that x would be 3 because 3x = 0 would be x = 3 to make x the subject

and then i did x-2 = 0 and then i got x = 2

so my answer was x = 3 or x = 2

but in the answer book it was x = 0 or x = 2

_______

i got two but im confused why its 0 and not 3?

Your fault: You're assuming x as 3, which ain't proper. You can't multiply both sides of an equation with 0 and claim LHS = RHS. lulz.

Simple way: 3x(x-2) = 0
=> Either x = 0 or x = 2. (3!=0)

Re: how to solve this quadratic? - THE_KNOWN - 05.10.2011

here :

easy :P