Is this even possible to have Integer value?

Algebra Level 4

A certain x x value in ( 2 , 3 ) (√2,√3) satisfies { 1 x } = { x 2 } . \{\frac{1}{x}\}=\{x^2\}.

Find P = x 4 3 x P=x^4-\frac{3}{x} .

Details
{ x } \{x\} is fractional part function.


The answer is 5.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

L.H.S. = 1 x [ 1 x ] = 1 x \frac{1}{x}-[\frac{1}{x}]=\frac{1}{x} , since x x lies between 2 , 3 \sqrt{2},\sqrt{3} , and its reciprocal is less than 1 1 .

R.H.S. = x 2 [ x 2 ] x^2-[x^2] . Now, 2 < x 2 < 3 [ x 2 ] = 2 2<x^2<3\Rightarrow[x^2]=2

Therefore, simplifying we get 2 x + 1 x = x 2 \frac{2x+1}{x}=x^2 . Adding and multiplying both sides by x x , we get ( x + 1 ) 2 = x 2 ( x + 1 ) (x+1)^2=x^2(x+1) . Since x + 1 0 x 2 x 1 = 0 x+1\neq0\Rightarrow x^2-x-1=0

Using the quadratic equation, we get x = 1 + 5 2 x=\frac{1+\sqrt{5}}{2} ,as the other root is discarded for being outside of the domain.

Thus, the value of P P with x = 1 + 5 2 x=\frac{1+\sqrt{5}}{2} , is 5 \boxed{5}

Sorry if my solution is too brief.

I like how it is the golden ratio.

Julian Poon - 6 years, 6 months ago

good solution.

Ayush Verma - 6 years, 7 months ago

Log in to reply

@Sanjeet Raria I think you love Golden section very much . This question is created by you am i right?

U Z - 6 years, 7 months ago

Log in to reply

No i didn't make it on my own. I've millions of books at my room this question belongs to one of them.

Yes I've been & still I'm fascinated by the brilliance of golden ratio. Last night me & Sandeep had a very productive discussion over it.

Sanjeet Raria - 6 years, 7 months ago

Nice solution...and I am too in love of the beautiful golden ratio....btw upvotes!!!!

rajdeep brahma - 3 years ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...