Problem: Given x = 3+$\sqrt{8}$, find the value $X^{2}+\frac{1}{^{X}}2$
View all: NATIONAL BANK ( PO) | WRITTEN QUESTION (MATH) SOLVE | 2015
Correct Answer: ans: 34.
Explanation:
Givenx = 3+$\sqrt{8}$……………(i)
=> $\frac{1}{x}$ = $\frac{1}{3+\sqrt{8}}$
=> $\frac{1}{x}$ =$\frac{3-\sqrt{8}}{(1+\sqrt{8})(3-\sqrt{8})}$
=> $\frac{1}{x}$ = $\frac{3-\sqrt{8}}{(3)^{2}-(\sqrt{8})^{2}}$
=> $\frac{1}{x}$ = $\frac{3-\sqrt{8}}{9-8}$
=> $\frac{1}{x}$ = $\frac{3-\sqrt{8}}{1}$
$\frac{1}{x}$ = (3-$\sqrt{8}$)……………………….(ii)
অতএব, (i) + (ii) হতে পাই
=> x+$\frac{1}{x}$ = (3+$(3+\sqrt{8)+(3-\sqrt{8})}$
=> x $\frac{1}{x}$ = 3+$\sqrt{8+3-\sqrt{8}}$
=> x $\frac{1}{x}$ = 6………………………………….(iii)
এখন, $x^{2}+\frac{1}{x^{2}}=(x+\frac{1}{x})^{2}-2x\times \frac{1}{x}$
= 6$^{2}$-2
= 36 -2
= 34