Hi all

I have a casio CFX-9850GC PLUS graphic calculator. I tried to solve the cubic: $\displaystyle 96x + 128x^3=0$ by inputting:

a= 128, b=0, c=96, d=0

My friend has a casio 9750 (cant remember any letters) and his solved the equation fine by getting 2, yet my calculator gets 0.866i and -0.866i.

Can anyone help me get the right answer at all? Firstly, I don't know what the 'i' bit is and I dont know why it isnt getting the correct answer?

Im new to graphic calculators, but this is over my head, and I've looked in the instruction manual but havent had any success.

I need this calculator my my Core 2 AS level maths exam in a few weeks, and I need to be completely sure that it is working properly and efficiently.

Many thanks!