Here, `b = 8`, so the period is `(2π)/8 = π/4.` To draw 2 cycles, we will need to graph from `0` to ` π/2` along the x-axis.

0.25π0.5π123-1-2-3xyOpen image in a new page

The graph of `y=3cos(8x)` for `0 ≤ x ≤ pi/2`

Note that we started the graph at `x = 0`, but we could have started anywhere. As long as we draw exactly 2 cycles, we are answering the question.

Now for interest, let's see what it looks like from `0` to 2π.

π123-1-2-3xyOpen image in a new page

The graph of `y=3cos(8x)` for `0 ≤ x ≤ 2pi`

Note that there are 8 cycles between `0` and 2π.