# Thread: Graphing the period of a trig function.

1. ## Graphing the period of a trig function.

I'm a bit confused. I know that to calculate the period you do 2pi/k but what if the question says y=1.5sin0.2pi x?

2pi/0.2pi = 2/0.2 = 10

How do I know where 10 is on a trig graph? I label my graph with pi/2, pi, 3pi/2, 2pi, etc. If there is no pi in the period how do I know where it would be on a graph?

2. Hello kmjt
Originally Posted by kmjt
I'm a bit confused. I know that to calculate the period you do 2pi/k but what if the question says y=1.5sin0.2pi x?

2pi/0.2pi = 2/0.2 = 10

How do I know where 10 is on a trig graph? I label my graph with pi/2, pi, 3pi/2, 2pi, etc. If there is no pi in the period how do I know where it would be on a graph?
Then don't label it like that! You have $\pi$ built in to your formula for $y$, so just label the $x$-axis with integer values. For instance, when $x = 5, 0.2\pi x = \pi$, so $y = 0$. And when $x = 2.5, 0.2\pi x = \pi/2$, so $y = 1.5$ (the maximum value). And a complete cycle will be between $x = 0$ and $x = 10$.