Some nasty algebra Watch

This discussion is closed.
ACarter
Badges: 0
#1
Report Thread starter 13 years ago
#1
Hi,

I was wondering if anyone could help with some equation manipulation :

How do I get from this equation :
g/2(H12-H22) + V12(H1-(H12/H2))=0

to :
g/2(H1+H2) + V12(H1/H2)(H1+H2)=0

?

My notes say something about dividing by (H1-H2) which I can do for the first term but not the second. Ignore where the formula comes from; I just need some help with the algebraic manipulation itself. Think I'm a bit rusty. Can anybody show me step by step ?

Many thanks,

Alan C.
0
MissSurfer
Badges: 2
Rep:
?
#2
Report 13 years ago
#2
Sorry, I can't help. But please could you tell me what level that is - like AS/A level or uni? It looks so hard!!
0
Gaz031
Badges: 15
Rep:
?
#3
Report 13 years ago
#3
Hi there, there seems to be either a typo in your post, one in your previous working or one in the answer you've been given.

\frac{9}{2}(H_{1}^{2}-H_{2}^{2})+V_{1}^2(H_{1}-\frac{H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{H_{1}H_{2}-H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{(H_{1})(H_{  2}-H_{1})}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})-V_{1}^2(\frac{H_{1}}{H_{2}})=0 (H_{1} \neq H_{2})

Sorry, I can't help. But please could you tell me what level that is - like AS/A level or uni? It looks so hard!!
You can do the part posted with A-Level maths, the actual techniques aren't that troublesome, perhaps the subscripts make it seem more confusing than it really is.
0
manps
Badges: 0
Rep:
?
#4
Report 13 years ago
#4
(Original post by Gaz031)
Hi there, there seems to be either a typo in your post, one in your previous working or one in the answer you've been given.

\frac{9}{2}(H_{1}^{2}-H_{2}^{2})+V_{1}^2(H_{1}-\frac{H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{H_{1}H_{2}-H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{(H_{1})(H_{  2}-H_{1})}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})-V_{1}^2(\frac{H_{1}}{H_{2}})=0 (H_{1} \neq H_{2})
how did you get from line 3 to 4? by cancelling by h1 - h2? something is wrong i think
0
Gaz031
Badges: 15
Rep:
?
#5
Report 13 years ago
#5
Dividing through by H_{1}-H_{2}. I'm fairly sure that nothing is wrong in the transition from line 3 to line 4 - remember \frac{H_{2}-H_{1}}{H_{1}-H_{2}}=-1
0
manps
Badges: 0
Rep:
?
#6
Report 13 years ago
#6
(Original post by Gaz031)
Hi there, there seems to be either a typo in your post, one in your previous working or one in the answer you've been given.

\frac{9}{2}(H_{1}^{2}-H_{2}^{2})+V_{1}^2(H_{1}-\frac{H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{H_{1}H_{2}-H_{1}^{2}}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})(H_{1}-H_{2})+V_{1}^2(\frac{(H_{1})(H_{  2}-H_{1})}{H_{2}})=0
\frac{9}{2}(H_{1}+H_{2})-V_{1}^2(\frac{H_{1}}{H_{2}})=0 (H_{1} \neq H_{2})


You can do the part posted with A-Level maths, the actual techniques aren't that troublesome, perhaps the subscripts make it seem more confusing than it really is.
let h1 = 1, h2 = 2 and v1 = 3
then in your line 1 this = -9
but in line 4 this = 9
0
Gaz031
Badges: 15
Rep:
?
#7
Report 13 years ago
#7
(Original post by manps)
let h1 = 1, h2 = 2 and v1 = 3
then in your line 1 this = -9
but in line 4 this = 9
It will be, I divided through by H_{1}-H_{2}(=-1) and of course \frac{-9}{-1}=9
0
manps
Badges: 0
Rep:
?
#8
Report 13 years ago
#8
(Original post by Gaz031)
It will be, I divided through by H_{1}-H_{2}(=-1) and of course \frac{-9}{-1}=9
oops overlooked that, i thought you were simplifying the equation...i.e the last line would be a tidier version equal to the first line.
:tsr:
0
HTale
Badges: 12
Rep:
?
#9
Report 13 years ago
#9
No, Gaz, you've made a mistake, just done it a different way
0
HTale
Badges: 12
Rep:
?
#10
Report 13 years ago
#10
(Original post by HTale)
No, Gaz, you've made a mistake, just done it a different way
Damn, shouldve pressed refresh
0
ACarter
Badges: 0
#11
Report Thread starter 13 years ago
#11
Thanks everyone. Looks like it was indeed a typo. Wrong term and wrong sign ! Good old lecturer ! It's actually university level Engineering (fluid mechanics - ugh !) but the algebra manipulation is A-Level standard, which bodes really well for me doesn't it about to start the 2nd year at uni !

I should have spotted that it was a typo, but you know that feeling when you've worked through something about 10 times and got the same result and your brain just stops working ?!

Alan C.
0
X
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Sheffield Hallam University
    City Campus Undergraduate
    Thu, 13 Dec '18
  • University of Buckingham
    Open Evening Undergraduate
    Thu, 13 Dec '18
  • University of Lincoln
    Mini Open Day at the Brayford Campus Undergraduate
    Wed, 19 Dec '18

Do you like exams?

Yes (207)
18.48%
No (681)
60.8%
Not really bothered about them (232)
20.71%

Watched Threads

View All