More x(s), more difficult, but not impossible, although.

What integer best fits in x?


The answer is 4.

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3 solutions

Chew-Seong Cheong
Jan 28, 2015

Since the R H S = 70737 256 1 RHS = \dfrac {70737}{256} \gg 1

x 4 70737 256 x 70737 256 4 = 4.0771 4 \Rightarrow x^4 \approx \dfrac {70737}{256} \quad \Rightarrow x \approx \sqrt [4] {\frac {70737}{256}} = 4.0771 \approx \boxed{4}

Omkar Kulkarni
Jan 27, 2015

I saw the denominator of the RHS as 256, and so I guessed four, but here's the solution.

Let a = x + 1 x a=x+\frac {1}{x}

x 2 + 1 x 2 = ( x + 1 x ) 2 2 = a 2 2 x^{2}+\frac {1}{x^{2}} = \left (x+\frac {1}{x} \right)^{2} - 2 = a^{2} - 2

x 4 + 1 x 4 = ( x 2 + 1 x 2 ) 2 2 = ( ( x + 1 x ) 2 2 ) 2 2 = ( a 2 2 ) 2 2 x^{4} + \frac {1}{x^{4}} = \left(x^{2} + \frac {1}{x^{2}} \right)^{2} - 2 = \left ( \left ( x+\frac {1}{x} \right)^{2} - 2 \right)^{2} - 2 = (a^{2} - 2)^{2} - 2

This you then substitute in the given equation, which becomes a degree four equation in a a , and once we have the value of a a , we can form a quadratic equation in x x and obtain the answer, 4 \boxed{4} .

Often ...after quickly solving prblm by reosonable guesses and then formulating a solution on the paper is becoming very popular in this culture of prblm solving .. I too did the same in this one ...:)

tanmay goyal - 6 years, 4 months ago
Tanmay Goyal
Feb 8, 2015

To quickly deduct the answer I jst saw the lrgest denominatr in the LHS ...which is in fact the LCM

Clearly it is x 4 x^{4} and is equal to 256

Now We see 25 6 1 / 4 = 4 256^{1/4} = 4

So the answer is 4

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