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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: To all certain as well as non certain elements
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sid.shah.90 (608)

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Solve\ the\ equation\\    (12x-1)(6x-1)(4x-1)(3x-1)=5

______________________________________________
Siddhant Shah


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anchitsaini (4377)

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on multiplying the eqn comes to be--

864x4 - 720x3 + 210x2 - 25x + 1 = 5

on observation / hit and trial

before getting this equation only we get x = 1/2 , - 1/12 as a solution

dividing the equation by (2x - 1)

we get --

432 x 3 - 144 x 2 + 33 x - 4 = 0

further dividing the equation by (12 x + 1)

we get --

108 x 2 - 45 x + 12 = 0

D = 45 2 - 4*108*12 <=0

hence the given equation has only 2 real roots and 2 imaginary roots

thus it is verified that  the answer is 1/2 , - 1/12 and there are not more answers

but this was a method just to verify , i still haven't got a proper method

Impossible To be Impossible is Impossible
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konichiwa2x (2388)

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Multiply first and last term, 2nd and 3rd term!





Substitute
 
This is a quadratic in t. Solve to get  or

or

giving you the solutions  

Guide to latex:
http://www.goiit.com/posts/list/community-shelf-a-guide-to-latex-48056.htm

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amaron (726)

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These type of equations can generally be solved by grouping the terms well.
 
Solve the equation\    (12x-1)(6x-1)(4x-1)(3x-1)=5
 
= (12x -1)(3x-1)*(6x-1)(4x-1)=5
 
implies
 
(36x2 -15x +1)*(24x2  - 10x +1)=5
 
take 12x2 - 5x =t
 
implies
 
(3t+1)(2t+1)=5
 
Now you can easily solve for t.
 
That solves the problem!
 
Edit:I didnt see konichiwa2x posted already.

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spideyunlimited (4254)

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(12x -1).(6x-1).(4x-1).(3x-1) = 5
Multiply both sides by 2 x 3

(12x - 1).(6x - 1).(12x - 3). (6x - 2) = 30

2.(6x - 1/2).(6x - 1). 2.(6x - 3/2). (6x - 2) = 30

(6x - 1/2).(6x - 1).(6x - 3/2). (6x - 2) = 30 / 4

let 6x - 2 = T
T.(T+1/2) (T+1) (T+3/2) = 30 / 4

Also notice 30/4 = 1*2*3*5 / 2*2
= (1) (3/2) (2) (5/2) ---------------------------(1)
OR
= (-1) (-3/2) (-2) (-5/2) ---------------------------(2)

Therefore T = 1 --------------by equating to (1)
or T = -5/2 ----------by equating to (2)

so 6x - 2 = 1
or 6x - 2 = -5/2

So x = 1/2 , -1/12

---------------------------------------------------------------

- Gaurav Ragtah (spideyunlimited)
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Decoder (899)

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a tidy little methos frm me..

rite it as (12x-1)(12x-2)(12x-3)(12x-4) = 120
let 12x= y

take y^2 - 5y = z..

put them and solve..
u get z = 16,-6
thus y = 6,-1 & two complex conjugates..
thus x= 1/2 ,-1/12..
just chill..

Don't Dream ..Do the dream...

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