What is the domain of this function. (Could someone explain it too? I wanna be able to do it myself as well)

What is the vertex form of f(x) = x2 + 6x + 3

Check all that apply. f is a function. f is a one-to-one function. c is a function. c is a one-to-one function.

Which equation shows the variable terms isolated on one side and the constant terms isolated on the other side for the equation -1/2x+3=4-1/4x? a. -1/4x=1 b. -3/4x=1 c. 7=1/4x d. 7=3/4x