<s>[INST] The graph of a quadratic equation from standard form is a parabola. The standard form of a quadratic equation is ax^2 + bx + c = 0. If the vertex of the parabola is at (h, k), then the vertex form of the quadratic equation can be written as a(x - h)^2 + k = 0. Which of the following quadratic equations represents the standard form of a parabola with vertex at (2, 1)?[/INST]