Find the solution to the equation 2 2 2 2 . . . − 1 = x .
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x = − 1 is not a valid solution to the equation. You introduced extraneous roots when squaring it.
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Indeed it is, was careless of me to check. Checked and fixed, thanks! :)
What is an extraneous root??
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It is a number obtained in the process of solving an equation that does not satisfy the equation.
Example of it is:
2 y + 7 + 4 = y
First, get the radical expression alone on one side of the equation: 2 y + 7 = y − 4
Squaring both sides to get rid of the radical on LHS: 2 y + 7 = ( y − 4 ) 2
Simplify the RHS: 2 y + 7 = y 2 − 8 y + 1 6
Compute y (put everything on one side): y 2 − 1 0 y + 9 = 0
Factorising it we obtain: ( y − 9 ) ( y − 1 ) = 0
Hence the solutions for y are , y = 9 , 1
But when plugging y=1 in the equation it wont work: 2 ( 1 ) + 7 + 4 = 1 is false!
Hence, y=1 is an extraneous root.
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@Mohammad Al Ali – I now also don't understand extraneous root
please help me
I just solved the radical first(solve a simpler problem) and got a quadratic with roots 0 and 2. Then dealt with subtracting one.
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Precisely! However, there is only one solution to this problem which is x = 1 , becareful with extraneous roots ;)
very impressive
√[2√[2[√2.... = (x + 1) square both sides
2(x + 1) = x² + 2x + 1
2x + 2 = x² + 2x + 1
x² = 1, x = ± 1
@Sunil pradhan -1 is an extraneous root...
Did it just this way(although had eliminated the inadmissable root).But took x-1 in place of x+1.Wont bother if any1 gives slang for such poor mistakes.It befits me.Urgh! Anyway although it seems i am d first person to vote for this solution i prefer it to those above.Looks simple.
2 (x + 1) = (x + 1)^2
=> (x + 1)^2 - 2 (x + 1) = 0
=> (x + 1)(x + 1 - 2) = 0
=> x = 1 as ? - 1 cannot be 0 - 1.
When we take square root of 2 we get 1,41,mutiply by 2 we get2.82,again squareroot we get 1.67 multiply by 2 and srareroot we get finally 4 whose squareroot is2 then take minus 1 so X =1 Ans K.K.GARG,India
Finally we get 4 .. how ? Can u tell me please :(
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So here is the solution..
2 2 2 2 . . . − 1 = x .
Let y = 2 2 2 . . .
Rewriting the equation we obtain,
y − 1 = x
Squaring both sides,
( y − 1 ) 2 = x 2
Expanding the brackets of the Left Hand Side we obtain,
y 2 − 2 y + 1 = x 2
Calculating for y 2 we get that it is ( 2 2 2 . . . ) 2
Or simply,
2 × 2 2 2 . . .
Calculating for 2 y we attain that it is 2 2 2 2 . . .
We notice here that y 2 = 2 y , and so the equation reduces to x 2 − 1 = 0
Hence by Difference Of Two Squares, ( x − 1 ) ( x + 1 ) = 0
However, x = -1 is not a valid solution (extraneous root)
And the solution is: x = 1