Range of x x

Algebra Level 2

( 1 3 ) x + 1 x 2 > 9 \Large \left(\frac{1}{3}\right)^\frac{|x|+1}{x-2} > 9

What values of x x satisfy the inequality above?

x ( 1 , 2 ) x \in (1,2) x ( 2 , 3 ) x \in (2,3) x [ 2 , 3 ) x \in [2,3) x R x \in \mathbb{R} x ( , 1 ) ( 3 , ) x \in (-\infty,1) \cup (3,\infty) x { 1 , 2 } x \in \{1,2\} No solutions

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1 solution

Andy Hayes
Dec 10, 2017

( 1 3 ) 2 = 9 , \left(\frac{1}{3}\right)^{-2}=9, and so the expression in the exponent must be less than 2 : -2:

x + 1 x 2 < 2 \frac{\vert x \vert +1}{x-2} < -2

Suppose that x > 2. x>2. Then,

x + 1 < 2 ( x 2 ) 3 x < 3 x < 1 A contradiction! \begin{aligned} x+1 &< -2(x-2) \\ 3x &< 3 \\ x &< 1 \quad {\color{#D61F06}\text{A contradiction!}} \end{aligned}

Now suppose that x < 2. x<2. Then,

x + 1 > 2 ( x 2 ) |x|+1 > -2(x-2)

If x > 0 : x>0:

x + 1 > 2 ( x 2 ) 3 x > 3 x > 1 \begin{aligned} x+1 &> -2(x-2) \\ 3x &> 3 \\ x &> 1 \\ \end{aligned}

If x < 0 : x<0:

x + 1 > 2 ( x 2 ) x > 3 A contradiction! \begin{aligned} -x+1 &> -2(x-2) \\ x &> 3 \quad {\color{#D61F06}\text{A contradiction!}} \end{aligned}

Therefore, the interval that satisfies the inequality is: x ( 1 , 2 ) . x \in (1,2).

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