Question

How can I prove that one of the roots of x^4-x^3+7x^2-9x-18, is 3i? When I plug 3i into x, it doesn't come out.

Answer 1

when x= 3i yuo dont get y=0?

Answer 2

I get -78-24i

Answer 3

0=3i^4-3i^3+7(3i)^2-9(3i)-18
0=3+3i-63-27i-18
0≠-78-24i

Answer 4

http://www.wolframalpha.com/input/?i=+%283i%29%5E4-%283i%29%5E3%2B7%283i%29%5E2-9%283i%29-18

Answer 5

Hmm it's 3^4 right?

Answer 6

x=3i

Answer 7

\[ (3i)^4-(3i)^3+7(3i)^2-9(3i)-18\]

Answer 8

wow i am an idiot... i forgot my parenthesis's thanks ishaan

Answer 9

you're welcome lol :-)