mathrepost
posted by Connie .
Which equation has the complex number 43i as a root?
(1) x^2+6x25=0
(2) x^26x+25=0
(3) x^2+8x25=0
(4) x^28x+25=0
I have no clue how to do it!!!PLEASE HELP!!!Please guide by step by step!!THANKS A LOT~!!!!

Look at the serds. To get a serd that is negative, you have to have a or c negative. That means only 1 or 3 can be correct. Now, which yields sqrt (b^24ac) to be 6i ?

I still don't get it