4 Views

Question : If $(x+\frac{1}{x})^2=3$, then the value of $x^{72}+x^{66}+x^{54}+x^{24}+x^6+1$ is:

Option 1: $0$

Option 2: $2$

Option 3: $3$

Option 4: $4$


Team Careers360 2nd Jan, 2024
Answer (1)
Team Careers360 22nd Jan, 2024

Correct Answer: $0$


Solution : Given: $(x+\frac{1}{x})^2=3$
We know that the algebraic identity is $(x+\frac{1}{x})^3=x^3+\frac{1}{x^3}+3(x+\frac{1}{x})$.
$(x+\frac{1}{x})^2=3$
By taking the square root on both sides of the above equation, we get,
$(x+\frac{1}{x})=\sqrt3$
By taking the cube on both sides of the above equation, we get,
$(x+\frac{1}{x})^3=(\sqrt3)^3$
⇒ $x^3+\frac{1}{x^3}+3(x+\frac{1}{x})=3\sqrt3$
Substitute the value of $(x+\frac{1}{x})=\sqrt3$ in above equation,
$x^3+\frac{1}{x^3}+3\sqrt3=3\sqrt3$
⇒ $x^3+\frac{1}{x^3}=3\sqrt3-3\sqrt3$
⇒ $x^3+\frac{1}{x^3}=0$
⇒ $x^6+1=0$
⇒ $x^6=–1$
Substitute the value of $x^6=–1$ in given expression,
$x^{72}+x^{66}+x^{54}+x^{24}+x^6+1$
$=(x^6)^{12}+(x^6)^{11}+(x^6)^{9}+(x^6)^{4}+x^6+1$
$=(–1)^{12}+(–1)^{11}+(–1)^{9}+(–1)^{4}+(–1)+1$
$=1-1-1+1-1+1=0$
Hence, the correct answer is $0$.

SSC CGL Complete Guide

Candidates can download this ebook to know all about SSC CGL.

Download EBook

Know More About

Related Questions

TOEFL ® Registrations 2024
Apply
Accepted by more than 11,000 universities in over 150 countries worldwide
Manipal Online M.Com Admissions
Apply
Apply for Online M.Com from Manipal University
GRE ® Registrations 2024
Apply
Apply for GRE® Test now & save 10% with ApplyShop Gift Card | World's most used Admission Test for Graduate & Professional Schools
View All Application Forms

Download the Careers360 App on your Android phone

Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile

150M+ Students
30,000+ Colleges
500+ Exams
1500+ E-books