Equations and Inequations

Algebra Level pending

a d b c

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2 solutions

Tom Engelsman
Oct 9, 2017

The above exponential equation can be rewritten as ( 3 3 ) 1 x + ( 2 2 3 1 ) 1 x = 2 ( 2 3 ) 1 x (3^3)^{\frac{1}{x}} + (2^{2}3^{1})^{\frac{1}{x}} = 2(2^3)^{\frac{1}{x}} , or ( 3 1 x ) 3 + ( 3 1 x ) ( 2 1 x ) 2 = 2 ( 2 1 x ) 3 . (3^{\frac{1}{x}})^3 + (3^{\frac{1}{x}})(2^{\frac{1}{x}})^2 = 2(2^{\frac{1}{x}})^3. Now, let u = 3 1 x , v = 2 1 x u = 3^{\frac{1}{x}}, v = 2^{\frac{1}{x}} so that we obtain the quadratic:

u 3 + u v 2 = 2 v 3 u^3 + uv^2 = 2v^3 ;

or u 3 v 3 = v 3 u v 2 u^3 - v^3 = v^3 - uv^2 ;

or ( u v ) ( u 2 + u v + v 2 ) = v 2 ( u v ) (u-v)(u^2 + uv + v^2) = -v^2 (u-v) ;

or u 2 + u v + 2 v 2 = 0 u^2 + uv + 2v^2 = 0 ;

or u = v ± v 2 4 ( 1 ) ( 2 v 2 ) 2 = v ± 7 v 2 2 = ( 1 ± 7 i 2 ) v u = \frac{-v \pm \sqrt{v^2 - 4(1)(2v^2)}}{2} = \frac{-v \pm \sqrt{-7v^2}}{2} = (\frac{-1 \pm \sqrt{7}i}{2}) \cdot v ;

or u v = ( 3 2 ) 1 x = 1 ± 7 i 2 \frac{u}{v} = (\frac{3}{2})^{\frac{1}{x}} = \frac{-1 \pm \sqrt{7}i}{2} .

Hence, we have the ratio of two real numbers equaling one of two non-zero complex numbers C O N T R A D I C T I O N \Rightarrow CONTRADICTION . There is no x R x \in \mathbb{R} that solves the above original exponential equation.

Thank you sir.

Aakhyat Singh - 3 years, 8 months ago
Aakhyat Singh
Oct 9, 2017

@Corina Margareta Cristian , @Tom Engelsman , how did u solve this question?? Pls share the solution.

Solution's posted, @Aakhyat Singh ......enjoy!

tom engelsman - 3 years, 8 months ago

I think that there is no real solution solve that equation because 27 and 8 has no common divisor other than 1 and for x = 1 the equation is not true. The equation is true just for x = ∞ , 1 /x = 0, and this is not a real solution

Corina Margareta Cristian - 3 years, 8 months ago

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