Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If (x3 + \(\frac{1}{x^3}\) - a)2 + (x + \(\frac{1}{x}\) - b)2 = 0, where a and b are real numbers and x ≠ 0, then \(\frac{a}{b}\) is equal to?

Options:

b2 + 1

b2 + 3

b2 - 3

b2 - 1

Correct Answer:

b2 - 3

Explanation:

(x3 + \(\frac{1}{x^3}\) - a)2 + (x + \(\frac{1}{x}\) - b)2 = 0

⇒ (x3 + \(\frac{1}{x^3}\) - a)2 = 0

⇒ x3 + \(\frac{1}{x^3}\) = a .... (i)

and 

⇒ (x + \(\frac{1}{x}\) - b)2 = 0

⇒ x + \(\frac{1}{x}\) = b

cubing both sides →

x3 + \(\frac{1}{x^3}\) + 3x × \(\frac{1}{x}\) (b) = b3

a + 3b = b3 (using ... (i))

a = b3 - 3b

Now, \(\frac{a}{b}\) = \(\frac{b^3 - 3b}{b}\) = b2 - 3