Exponential inequality

Algebra Level 1

Suppose that α < x < β \alpha < x< \beta is the solution to the following inequality: ( 1 3 ) x 2 + 1 > ( 1 9 ) x + 2 . \left(\frac{1}{3}\right)^{x^2+1} > \left(\frac{1}{9}\right)^{x+2}. Then what is the value of β α ? \beta - \alpha ?


The answer is 4.

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2 solutions

Aquilino Madeira
Jul 22, 2015

( 1 3 ) x 2 + 1 > ( 1 9 ) x + 2 ( 3 1 ) x 2 + 1 > ( 3 2 ) x + 2 ( 3 ) x 2 1 > ( 3 ) 2 x 4 x 2 1 > 2 x 4 x 2 + 2 x + 3 > 0 x 2 2 x 3 < 0 1 < x < 3 β α = 3 ( 1 ) = 4 \begin{array}{l} {\left( {\frac{1}{3}} \right)^{{x^2} + 1}} > {\left( {\frac{1}{9}} \right)^{x + 2}}\\ \Leftrightarrow {\left( {{3^{ - 1}}} \right)^{{x^2} + 1}} > {\left( {{3^{ - 2}}} \right)^{x + 2}}\\ \Leftrightarrow {\left( 3 \right)^{ - {x^2} - 1}} > {\left( 3 \right)^{ - 2x - 4}}\\ \Leftrightarrow - {x^2} - 1 > - 2x - 4\\ \Leftrightarrow - {x^2} + 2x + 3 > 0\\ \Leftrightarrow {x^2} - 2x - 3 < 0\\ \Leftrightarrow - 1 < x < 3\\ \\ \to \beta - \alpha = 3 - ( - 1) = 4 \end{array}

Mayank Holmes
Jun 28, 2014

the answer is wrong ! the solution to this equation would be : x belongs to (- infinity to -1) U ( 3 to +infinity)

Remember not to assume that the inequality sign will the same "direction"

Ian Limarta - 5 years, 3 months ago

You did wrong at 2(x+2) part... I did the same mistake and got that answer.

Suryanshu Sharma - 4 years, 8 months ago

Log in to reply

Sorry about that I made a mistake

Suryanshu Sharma - 4 years, 8 months ago

x=(1,3) or {x/1<x<3}

Edith Valerio - 4 years, 6 months ago

Your answer is wrong. 4 is the correct answer

布拉 辛格 - 1 year ago

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