Question

How to plot the graph of y = cos pi x ?

Answer 1

The plot is as follows

graph{cos(pi*x) [-10, 10, -5, 5]}

Answer 2

The period of cos kx is 2`pi`/k. So, the period of cos 2x is 2.The amplitude is 1.

Explanation:

For one complete cosine wave:
x: 0 1/2 1 3/2 2
y: 1 0 `-`1 0 1

y repeats when x is increased or decreased by 2.