Question 6598
Great job, both in solving the problem as well as in using my formula system. 

your step 5 is wrong, the answer is {{{x=-1 +- sqrt( -16 )/2 }}}, (you forgot /2)or

{{{x=-1+- 2sqrt(-1)}}}. 

You should re-read the complex numbers chapter, where they explain what i is (i can be thought of as sqrt(-1).