Question

Plot a graph for the equation $y=x^2-4x$.

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 $y=-4$
$\Rightarrow Vertex=(2,-4)$. 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.
Now, sketch the parabola as shown in the figure.