Concept understanding — Quadratic Equations with Complex Roots
Every quadratic equation ax2+bx+c=0 (with a=0) has solutions given by the familiar formula x=2a−b±b2−4ac, and this formula continues to work even when the discriminant D=b2−4ac is negative or when the coefficients a,b,c are themselves complex — the Fundamental Theorem of Algebra guarantees that a degree-n polynomial equation always has exactly n roots in the complex numbers, so a quadratic is never left without a solution. When a,b,c are real and D<0, the square root D is rewritten as i∣D∣, and the two roots that come out are complex conjugates of each other — if p+iq is one root, p−iq is automatically the other. When the coefficients are themselves complex (or when the discriminant is a general complex number rather than a negative real one), finding D requires the square-root-of-a-complex-number technique (writing the square root as a+ib and solving two simultaneous equations), and the two r …