Solve for real x
( 1 2 x − 1 ) ( 6 x − 1 ) ( 4 x − 1 ) ( 3 x − 1 ) = 5
If α and β are its zeroes, then enter your answer as α β 1 .
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Don't say a sorry for just that.! By the way , how did you solve the problem? Same method?
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I did it by the long method. Multiplying all and then factorise and all...
Your method is short and nice. :)
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But , that factorization would have been pretty tough. Just like the problem , even the solution is also not mine. :( :(
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@Ankit Kumar Jain – Yes.. that actually makes the problem hard. ( Level 4)
How is anyone supposed to even think like that? Did you just randomly multiplied numbers or there was any insight
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The motive was to convert that biquadratic to some quadratic. This can be done in this way that you are somehow able to use this identity ( a + b ) ( a − b ) = a 2 − b 2 .
So , we need to make the coeff's of x in all the terms equal and then let some term to be a so that we can get a quadratic in a 2 .
I hope that it clarifies your doubt..:):)
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And the question seemed to be quite defined in this way because after you make the coefficients equal you can easily see the term which you require to as a
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We can rewrite the equation as 2 ( 1 2 x − 1 ) 4 ( 6 x − 1 ) 6 ( 4 x − 1 ) 8 ( 3 x − 1 ) = 5 ⋅ 2 ⋅ 4 ⋅ 6 ⋅ 8
⇒ ( 2 4 x − 2 ) ( 2 4 x − 4 ) ( 2 4 x − 6 ) ( 2 4 x − 8 ) = 1 9 2 0
Let 2 4 x − 5 = a
Then , our equation becomes ( a − 3 ) ( a − 1 ) ( a + 1 ) ( a + 3 ) = 1 9 2 0
⇒ ( a 2 − 1 ) ( a 2 − 9 ) = 1 9 2 0
⇒ a 4 − 1 0 a 2 − 1 9 1 1 = ( a 2 + 3 9 ) ( a 2 − 4 9 ) = 0
⇒ a 2 = − 3 9 , 4 9
But since we want real solutions , we reject a 2 = − 3 9
⇒ a 2 = 4 9 ⇒ a = ± 7 ⇒ 2 4 x − 5 = ± 7
⇒ x = 2 1 , 1 2 − 1
Required answer is − 2 4