Point 4 — Sum and product of roots

Sum and product of roots; roots given and a coefficient unknown.

If α and β are the roots of ax² + bx + c = 0, then:

• Sum of roots (α + β) = −$\frac{b}{a}$
• Product of roots (αβ) = $\frac{c}{a}$

If α, β, δ are the roots of ax³ + bx² + cx + d = 0, then:

• Sum of roots (α + β + δ) = $\frac{-b}{a}$
• Product of roots αβδ = −$\frac{d}{a}$