import kotlin.math.*

fun Point.rotate(theta: Double) {
    val x0 = x 
    val y0 = y
    x = x0 * cos(theta) - y0 * sin(theta)
    y = x0 * sin(theta) + y0 * cos(theta) 
}

fun main() {
    val p = Point(1.0, 0.0)
    p.rotate(PI / 6)
    p.show()
}