If $${x^2} + \frac{1}{{25{x^2}}} = \frac{8}{5}$$ and x > 0, then what is the value of $${x^3} + \frac{1}{{125{x^3}}} = ?$$
A. 7√2
B. 5√2
C. $$\frac{{7\sqrt 2 }}{5}$$
D. 7√6
Answer: Option C
Solution(By Examveda Team)
$$\eqalign{ & \because \,{x^2} + \frac{1}{{25{x^2}}} = \frac{8}{5} \cr & \Rightarrow {x^2} + \frac{1}{{25{x^2}}} + 2x \times \frac{1}{{5x}} = \frac{8}{5} + \frac{2}{5} \cr & \Rightarrow {\left( {x + \frac{1}{{5x}}} \right)^2} = 2 \cr & \Rightarrow x + \frac{1}{{5x}} = \sqrt 2 \cr & {\text{On cubing both sides}} \cr & \Rightarrow {x^3} + \frac{1}{{125{x^3}}} + 3 \times \frac{1}{5}\left( {\sqrt 2 } \right) = {\left( {\sqrt 2 } \right)^3} \cr & \Rightarrow {x^3} + \frac{1}{{125{x^3}}} = 2\sqrt 2 - \frac{{3\sqrt 2 }}{5} \cr & \Rightarrow {x^3} + \frac{1}{{125{x^3}}} = \frac{{7\sqrt 2 }}{5} \cr} $$Related Questions on Algebra
If $$p \times q = p + q + \frac{p}{q}{\text{,}}$$ then the value of 8 × 2 is?
A. 6
B. 10
C. 14
D. 16
A. $$1 + \frac{1}{{x + 4}}$$
B. x + 4
C. $$\frac{1}{x}$$
D. $$\frac{{x + 4}}{x}$$
A. $$\frac{{20}}{{27}}$$
B. $$\frac{{27}}{{20}}$$
C. $$\frac{6}{8}$$
D. $$\frac{8}{6}$$
Join The Discussion