Complex Numbers And Quadratic Equations question 405
Question: If $ x=3+i $ , then $ x^{3}-3x^{2}-8x+15= $ [UPSEAT 2003]
Options:
A) 6
B) 10
C) - 18
D) - 15
Show Answer
Answer:
Correct Answer: D
Solution:
$ x=3+i\Rightarrow x-3=i $
$ \Rightarrow $ $ x^{2}-6x+10=0 $
Þ $ x^{3}-3x^{2}-8x+15 $ $ =x(x^{2}-6x+10)+3(x^{2}-6x+10)-15 $ $ =x(0)+3(0)-15=-15 $ .
BETA
