Question

What is the vertex of the graph of y = x2 + 4x?

Answer 1

a=1,b=−4. As a is positive, the parabola should open up.

As c=0, the parabola passes through the origin.

Vertex: x=−b/2a=2, so y=−4

⇒Vertex=(2,−4). Assuming two values of x,

x 1 0

y −3 0

Points obtained: (2,−4),(1,−3),(0,0).

Symmetry of parabola: Mirror image.

Points of (1,−3) and (0,0) are (3,−3) and (4,0), respectively.