Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If x2 - 25x - 1= 0

 and x > 1, then the value of

x3 - \(\frac{1}{x^3}\) will be:

Options:

15625

15700

15678

14533

Correct Answer:

15700

Explanation:

If x2 - 25x - 1= 0

Divide by x on both sides,

x -  \(\frac{1}{x}\) = 25

x3 - \(\frac{1}{x^3}\)  = 253 + 3 × 25 = 15700

 

Note - if x -  \(\frac{1}{x}\) = a

then x3 - \(\frac{1}{x^3}\) =  a3 + 3a