Complex Numbers And Quadratic Equations question 714
Question: The roots of the equation $ x^{4}-8x^{2}-9=0 $ are
Options:
A) $ \pm 3,\ \pm 1 $
B) $ \pm 3,\ \pm i $
C) $ \pm 2,\ \pm i $
D) None of these
Show Answer
Answer:
Correct Answer: B
Solution:
Equation $ x^{4}-8x^{2}-9=0 $
Þ $ x^{4}-9x^{2}+x^{2}-9=0 $
Þ $ x^{2}(x^{2}-9)+1(x^{2}-9)=0 $
Þ $ (x^{2}+1)(x^{2}-9)=0\Rightarrow x=\pm i,\pm 3 $ .
BETA
