Q.Find the quadratic equation whose roots are $-3 \pm 5i$.

A quadratic expression $ax^2+bx+c$ ($a \neq 0$) is the algebraic backbone behind parabolas, and this chapter builds every tool needed to reason about it: the roots and the discriminant that classifies them, the neat sum/product relations that connect roots to coefficients, and the sign-and-extreme-value behaviour that lets us decide where the expression is positive, negative, or at its largest/smal …