Chapter 8 - Graphing Quadratic Functions - 8.4 - Graphing f(x) = a(x-h)^2 + k - Exercises - Page 446: 19

Vertex: $(-1,0)$ Axis of symmetry $x=-1$

The quadratic function in the form $y=a(x-h)^2+k$ has the vertex $(h,k)$ and the axis of symmetry $x=h$. $$f(x)=3(x+1)^2$$ Rewrite as: $$f(x)=3(x-(-1))^2+0$$ Therefore $h=-1$, $k=0$. The vertex is: $$(h,k)=(-1,0).$$ The axis of symmetry is: $$x=-1.$$