Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If x2 - 4x + 1 = 0 find x9 + x7 - 194x5 - 194x3

Options:

4

2\(\sqrt {3}\)

-4

-2\(\sqrt {3}\)

Correct Answer:

-4

Explanation:

x2 - 4x + 1 = 0

⇒ x + \(\frac{1}{x}\) = 4

If x + \(\frac{1}{x}\) = 4

x2 + \(\frac{1}{x^2}\) = x2 - 2

⇒ x2 + \(\frac{1}{x^2}\) = 14

⇒ x4 + \(\frac{1}{x^4}\) = 196  Put in find

⇒ x9 + x7 - (x4 + \(\frac{1}{x^4}\))x5 - (x4 + \(\frac{1}{x^4}\))x3

⇒ x9 + x7 - x9 - x - x7 - \(\frac{1}{x}\)

-x - \(\frac{1}{x}\) = -\(\left(x+\frac{1}{x}\right)\) = -4