this is an upward opening parabola. its minimum value occurs at the vertex. so that is what you need to find.

there are two main ways to find this without using calculus. you can use the vertex formula, or complete the square. which have you learnt in class?

this is a polynomial, its domain is all real x, as is the domain of all polynomials.b What is the domain of this function?

remember, the domain is the set of all input values (in this case, x-values) for which a function is defined