Nataliya D. answered 03/23/13
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ax2 + bx + c = 0
x12 = (-b ± √D) / 2a , D = b2 - 4ac
x2 - 6x + 13 = 0
a = 1 , b = (-6) , c = 13
D = (-6)2 - 4 · 1 · 13 = -16
x12 = (-(-6) ± 4i) / 2 ---> x12 = 3 ± 2i