If x2 - 15x + 1 = 0, what is the value of x4 - 223x2 + 6?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 5.
Given, x2 - 15x + 1 = 0
⇒ x + 1/x = 15
Squarying both sides,
⇒ x2 + 1/x2 + 2 = 225
⇒ x2 + 1/x2 = 223
Putting this value in given expression,
⇒ x4 - (x2 + 1/x2)x2 + 6
⇒ x4 - x4 - 1 + 6 = 5