Key ideas For f(x)=ax2+bx+cf(x)=ax^2+bx+cf(x)=ax2+bx+c: h=−b2a,k=f(h) h=-\frac{b}{2a},\qquad k=f(h)h=−2ab,k=f(h) Vertex: (h,k)(h,k)(h,k) If a>0a>0a>0 then range is [k,∞)[k,\infty)[k,∞) If a<0a<0a<0 then range is (−∞,k](-\infty,k](−∞,k] Domain is always R\mathbb{R}R for quadratic polynomials.