rotate method
Implementation
void rotate(num radians) {
final newHeading = heading + radians;
final magnitude = mag;
x = magnitude * cos(newHeading);
y = magnitude * sin(newHeading);
}
void rotate(num radians) {
final newHeading = heading + radians;
final magnitude = mag;
x = magnitude * cos(newHeading);
y = magnitude * sin(newHeading);
}