Question : If $x^4+\frac{1}{x^4}=1154$, where $x>0$, then what is the value of $x^3+\frac{1}{x^3}?$
Option 1: 205
Option 2: 214
Option 3: 185
Option 4: 198
Correct Answer: 198
Solution : Given, $x^4+\frac{1}{x^4}=1154$ Adding 2 on both sides, $x^4+\frac1{x^4}+2=1154+2$ ⇒ $(x^2)^2+(\frac1{x^2})^2+2\times x^2\times\frac1{x^2}=1156$ We know, $a^2+b^2+2ab=(a+b)^2$ ⇒ $(x^2+\frac{1}{x^2})^2=1156$ ⇒ $x^2+\frac{1}{x^2}=\sqrt{1156}$ ⇒ $x^2+\frac{1}{x^2}=34$ Again, adding 2 on both sides, ⇒ $x^2+\frac{1}{x^2}+2=34+2$ ⇒ $(x+\frac{1}{x})^2=36$ ⇒ $x+\frac{1}{x}=6$ We know, $a^3+b^3=(a+b)(a^2-ab+b^2)$ ⇒ $x^3+\frac{1}{x^3}=(x+\frac1x)(x^2-x\times\frac1x+\frac1{x^2})$ $= (x+\frac1x)(x^2+\frac1{x^2}-1)$ $= 6 × (34 – 1) = 6 × 33 = 198$ Hence, the correct answer is 198.
Result | Eligibility | Application | Selection Process | Cutoff | Admit Card | Preparation Tips
Question : If $x^4+x^{-4}=47, x>0$, then what is the value of $x+\frac{1}{x}-2?$
Question : If $x^2+\frac{1}{x^2}=\frac{7}{4}$ for $x>0$; then what is the value of $x+\frac{1}{x}$?
Question : If $x^4+x^{-4}=194, x>0$, then the value of $x+\frac{1}{x}$ is:
Question : If $x^2+\frac{1}{x^2}=\frac{7}{4}$ for $x>0$, what is the value of $(x^3+\frac{1}{x^3})$?
Question : If $x^2+6x+1=0$, then the value of $(x+6)^3+\frac{1}{(x+6)^3}$ = ?
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile