Quad-Rootika

Algebra Level 5

x + 3 4 x 1 + x + 8 6 x 1 = 1 \large\sqrt{x+3-4\sqrt{x-1}}+\sqrt{x+8-6\sqrt{x-1}}=1

How many real solution(s) exist for the above equation?

Only one solution. Two solutions. None of the given choices. No solution. Infinite.

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1 solution

Sandeep Bhardwaj
Jun 6, 2015

Let us assume that x 1 = t x = t 2 + 1 \sqrt{x-1}=t \implies x=t^2+1

Now the given equation is equivalent to :

t 2 + t 4 t + t 2 9 6 t = 1 \sqrt{t^2+t-4t}+\sqrt{t^2-9-6t}=1

( t 2 ) 2 + ( t 3 ) 2 = 1 \implies \sqrt{(t-2)^2}+\sqrt{(t-3)^2}=1

t 2 + t 3 = 1 \implies |t-2|+|t-3|=1

As we can see from the graph below, the above equation is satisfied for all values of y lying between 2 2 and 3 3 both inclusive.

So the solution is : 2 t 3 5 x 10 2 \leq t \leq 3 \implies 5 \leq x \leq 10

So, total number of real values of x x lying between 5 5 and 10 10 both inclusive is infinite.

enjoy !

Moderator note:

The iterated root of x 1 \sqrt{ x-1} strongly suggests to make the given substitution.

Simple standard solution.

Nice question as well as solution.

Ayush Verma - 5 years, 11 months ago

A silly mistake got me to wrong answer :((

Sahil Silare - 3 years, 2 months ago

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