someone solve this maths for me

knip · 14 Feb 2008 at 18:36

Ok so im trying to help out a mate whos had a really stressful week, can someone solve these two maths puzzles for me

3x 3 + 11x 2 -6x -8 =0

2x 3 +13x 2 -24x +9=0

The little 3 and 2 are squared and cubed.

Please help!
Fanks

geuben · 14 Feb 2008 at 18:38

Look for the powertoys for windows XP and get the graphical calculator one, that should let you solve them.

Edit: or use this http://www.1728.com/cubic.htm

stevenazari1 · 14 Feb 2008 at 18:40

I knew I shouldnt have clicked this thread >.<

iamdjdz · 14 Feb 2008 at 18:41

The first one is x=0.32
second is x = -1.125

i think - correct if wrong.

geuben · 14 Feb 2008 at 18:44

iamdjdz said:
The first one is x=0.32
second is x = -1.125

i think - correct if wrong.

There are multiple roots (solutions) to each one.

coolpunkskater · 14 Feb 2008 at 18:45

is this your GCSE or A level home work?
lol

knip · 14 Feb 2008 at 18:48

coolpunkskater said:
is this your GCSE or A level home work?
lol

Im 28 so its neither sorry!
Shes 22, but shes had a rough week as I said, and she asked if there was anything I could do to help.

Tombstone · 14 Feb 2008 at 18:48

Tell you whats really sad, 17 years ago I did A-Level Maths, and I cant remember at all how to do this.

Guess that was 2 years wasted of my youth

iamdjdz · 14 Feb 2008 at 18:49

knip said:
Im 28 so its neither sorry!
Shes 22, but shes had a rough week as I said, and she asked if there was anything I could do to help.

do you need the solutions?

I'm not great at maths but it should be ok?

knip · 14 Feb 2008 at 18:49

iamdjdz said:
do you need the solutions?

I'm not great at maths but it should be ok?

I need the solutions yes please!

She needs all the working too

geuben · 14 Feb 2008 at 18:50

Tombstone said:
Tell you whats really sad, 17 years ago I did A-Level Maths, and I cant remember at all how to do this.

Guess that was 2 years wasted of my youth

Doing them by hand takes effort, I just used to put them in my graphically calculator. Although when it came to exams where you weren't allowed the graphical calculators i was a bit stuck.

mrmoose · 14 Feb 2008 at 18:51

geuben said:
this http://www.1728.com/cubic.htm

cheers for that link will help me out when plotting awkward functions

iamdjdz · 14 Feb 2008 at 18:52

Right I got:

1)

3x 3 + 11x 2 -6x -8 =0
9x + 22x - 6x -8 = 0
25x - 8 = 0
25x = 8
x = 0.32

2)
2x 3 +13x 2 -24x +9=0
6x + 26x - 24x +9 = 0
8x +9 =0
8x = -9
x = -1.125

Again could be totally wrong.

geuben · 14 Feb 2008 at 18:53

iamdjdz said:
Right I got:

1)

3x 3 + 11x 2 -6x -8 =0
9x + 22x - 6x -8 = 0
25x - 8 = 0
25x = 8
x = 0.32

2)
2x 3 +13x 2 -24x +9=0
6x + 26x - 24x +9 = 0
8x +9 =0
8x = -9
x = -1.125

Again could be totally wrong.

Yep, Totally wrong; No offence. I think you misread the question.

hendrix · 14 Feb 2008 at 18:54

iamdjdz said:
Right I got:

1)

3x 3 + 11x 2 -6x -8 =0
9x + 22x - 6x -8 = 0
25x - 8 = 0
25x = 8
x = 0.32

2)
2x 3 +13x 2 -24x +9=0
6x + 26x - 24x +9 = 0
8x +9 =0
8x = -9
x = -1.125

Again could be totally wrong.

I think the 3 and 2 in the original are powers, so yes, totally wrong i'm afraid

iamdjdz · 14 Feb 2008 at 18:54

geuben said:
Yep, Totally wrong; No offence. I think you misread the question.

Right - I told you I'd be wrong - what are the correct solutions lol at least I'd a go.

|Ric| · 14 Feb 2008 at 18:54

first one:
x = 1, x = -4, x = -2/3

second one:
x = 1, x = (-15 +/- sqrt(297)) / 4

geuben · 14 Feb 2008 at 18:55

iamdjdz said:
Right - I told you I'd be wrong - what are the correct solutions lol at least I'd a go.

You can get the answers on the link i posted, theres also the method to solve them on there too.

Edit: Im not sure how the calculator in the link handles imaginary numbers, if you google for "cubic equation solver" theres a few others.

Duke · 14 Feb 2008 at 18:56

stevenazari1 said:
I knew I shouldnt have clicked this thread >.<

Did you get a headache too?

iamdjdz · 14 Feb 2008 at 18:56

geuben said:
You can get the answers on the link i posted, theres also the method to solve them on there too.

Lol I get where I misread it actually - tbh I don't understand how to use the link and do it. My maths skills suck.