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

Explanation

`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`
`implies 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 figure