What Happens As We Go Deeper?

Algebra Level 2

x , x , x , x \sqrt x , \qquad \sqrt{\sqrt x}, \qquad \sqrt{\sqrt{\sqrt x}} , \qquad \sqrt{\sqrt{\sqrt{\sqrt x}}}

If 0 < x < 1 0 < x < 1 , which of the numbers above is the largest?

x \sqrt x x \sqrt{\sqrt x} x \sqrt{\sqrt{\sqrt x}} x \sqrt{\sqrt{\sqrt{\sqrt x}}}

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.

3 solutions

P C
Mar 17, 2016

Considering x x = x 1 2 x 1 4 = x 1 4 ( x 2 1 ) < 0 ( S i n c e x < 0 ) \sqrt{x}-\sqrt{\sqrt{x}}=x^{\frac{1}{2}}-x^{\frac{1}{4}}=x^{\frac{1}{4}}(x^2-1)<0 \ \ (Since \ x<0)

With x x \sqrt{\sqrt{x}}-\sqrt{\sqrt{\sqrt{x}}} and x x \sqrt{\sqrt{\sqrt{x}}}-\sqrt{\sqrt{\sqrt{\sqrt{x}}}} we get the same results x > x > x > x \therefore \sqrt{\sqrt{\sqrt{\sqrt{x}}}}>\sqrt{\sqrt{\sqrt{x}}}>\sqrt{\sqrt{x}}>\sqrt{x}

Amr Abdelnoor
Mar 24, 2016

Leon Eschle
Feb 24, 2020

We start by proving that, if 0 < x < 1 0<x<1 , then x < x x<\sqrt{x} :

Notice that for any number x x , such that 0 < x < 1 0<x<1 , x 2 < x x^2<x (a fraction of a positive real number is evidently smaller than the positive number itself). If we now take the square root on both sides, we obtain: x < x x<\sqrt{x}

If we again take the square root on both sides 3 times, we obtain 3 more inequalities:

x < x \sqrt{x}<\sqrt{\sqrt{x}}

x < x \sqrt{\sqrt{x}}<\sqrt{\sqrt{\sqrt{x}}}

x < x \sqrt{\sqrt{\sqrt{x}}}<\sqrt{\sqrt{\sqrt{\sqrt{x}}}}

Now we combine all 4 inequalities and it follows that: x < x < x < x \sqrt{x}<\sqrt{\sqrt{x}}<\sqrt{\sqrt{\sqrt{x}}}<\sqrt{\sqrt{\sqrt{\sqrt{x}}}}

Q.E.D

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...