I'm assuming you mean and not .
If you know the graph of the basic sine function, you would know that the x-intercepts are , for any integer n (in other words, multiples of pi). Putting a number greater than 1 in front of x transforms the graph -- you have a horizontal shrink by a factor of that number. So in our case, is a horizontal shrink of by a factor of 2.
This effectively means that the x-intercepts occur twice as often, ie. , for any integer n.
Another example: say it's . Then its x-intercepts would be , for any integer n.