Se da la desigualdad:
x − 2 x − 2 ≤ 3 \sqrt{x} - \frac{2}{\sqrt{x - 2}} \leq 3 x − x − 2 2 ≤ 3 Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
x − 2 x − 2 = 3 \sqrt{x} - \frac{2}{\sqrt{x - 2}} = 3 x − x − 2 2 = 3 Resolvemos:
x 1 = − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 11 2 x_{1} = \frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{11}{2} x 1 = 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 2 11 x 1 = − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 11 2 x_{1} = \frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{11}{2} x 1 = 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 2 11 Las raíces dadas
x 1 = − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 11 2 x_{1} = \frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{11}{2} x 1 = 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 2 11 son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
x 0 ≤ x 1 x_{0} \leq x_{1} x 0 ≤ x 1 Consideremos, por ejemplo, el punto
x 0 = x 1 − 1 10 x_{0} = x_{1} - \frac{1}{10} x 0 = x 1 − 10 1 =
− 1 10 + ( − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 11 2 ) - \frac{1}{10} + \left(\frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{11}{2}\right) − 10 1 + 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 2 11 =
− 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 27 5 \frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{27}{5} 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 5 27 lo sustituimos en la expresión
x − 2 x − 2 ≤ 3 \sqrt{x} - \frac{2}{\sqrt{x - 2}} \leq 3 x − x − 2 2 ≤ 3 − 2 − 2 + ( − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 27 5 ) + − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 27 5 ≤ 3 - \frac{2}{\sqrt{-2 + \left(\frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{27}{5}\right)}} + \sqrt{\frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{27}{5}} \leq 3 − − 2 + 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 5 27 2 + 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 5 27 ≤ 3 ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
/ __________________________________________________________________________________________________________________________________________________
/ / ______________________
/ / 130 / 35119 ______ 288 1823
/ / --- - 2*3 / - ----- + 8*\/ 2442 + --------------------------------------------------------------------------- + -----------------------------
/ ___________________________________________________________________ / 3 \/ 216 ___________________________________________________________________ ______________________
/ / ______________________ / / ______________________ / 35119 ______
/ / 65 / 35119 ______ 1823 / / 65 / 35119 ______ 1823 18*3 / - ----- + 8*\/ 2442
/ / -- + 2*3 / - ----- + 8*\/ 2442 - ----------------------------- / / -- + 2*3 / - ----- + 8*\/ 2442 - ----------------------------- \/ 216
/ / 3 \/ 216 ______________________ / / 3 \/ 216 ______________________
/ / / 35119 ______ / / / 35119 ______
/ / 18*3 / - ----- + 8*\/ 2442 / / 18*3 / - ----- + 8*\/ 2442
/ 27 \/ \/ 216 \/ \/ \/ 216 2
/ -- + --------------------------------------------------------------------------- + -------------------------------------------------------------------------------------------------------------------------------------------------------------- - ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\/ 5 2 2 ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ <= 3
/ __________________________________________________________________________________________________________________________________________________
/ / ______________________
/ / 130 / 35119 ______ 288 1823
/ / --- - 2*3 / - ----- + 8*\/ 2442 + --------------------------------------------------------------------------- + -----------------------------
/ ___________________________________________________________________ / 3 \/ 216 ___________________________________________________________________ ______________________
/ / ______________________ / / ______________________ / 35119 ______
/ / 65 / 35119 ______ 1823 / / 65 / 35119 ______ 1823 18*3 / - ----- + 8*\/ 2442
/ / -- + 2*3 / - ----- + 8*\/ 2442 - ----------------------------- / / -- + 2*3 / - ----- + 8*\/ 2442 - ----------------------------- \/ 216
/ / 3 \/ 216 ______________________ / / 3 \/ 216 ______________________
/ / / 35119 ______ / / / 35119 ______
/ / 18*3 / - ----- + 8*\/ 2442 / / 18*3 / - ----- + 8*\/ 2442
/ 17 \/ \/ 216 \/ \/ \/ 216
/ -- + --------------------------------------------------------------------------- + --------------------------------------------------------------------------------------------------------------------------------------------------------------
\/ 5 2 2 significa que la solución de la desigualdad será con:
x ≤ − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + − 2 − 35119 216 + 8 2442 3 + 1823 18 − 35119 216 + 8 2442 3 + 130 3 + 288 − 1823 18 − 35119 216 + 8 2442 3 + 2 − 35119 216 + 8 2442 3 + 65 3 2 + 11 2 x \leq \frac{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}{2} + \frac{\sqrt{- 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + \frac{130}{3} + \frac{288}{\sqrt{- \frac{1823}{18 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}}} + 2 \sqrt[3]{- \frac{35119}{216} + 8 \sqrt{2442}} + \frac{65}{3}}}}}{2} + \frac{11}{2} x ≤ 2 − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 + 2 − 2 3 − 216 35119 + 8 2442 + 18 3 − 216 35119 + 8 2442 1823 + 3 130 + − 18 3 − 216 35119 + 8 2442 1823 + 2 3 − 216 35119 + 8 2442 + 3 65 288 + 2 11 _____
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