You can't retrieve the intent during class instansiation.
Change your code to something like this...
public class NewActivity extends Activity {
Intent i;
TextView bb;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.new_activity);
i = getIntent();
Double a = i.getExtras().getDouble("a");
Double b = i.getExtras().getDouble("b");
Double c = i.getExtras().getDouble("c");
Double D = i.getExtras().getDouble("D");
Double x1 = i.getExtras().getDouble("x1");
Double x2 = i.getExtras().getDouble("x2");
bb = (TextView) findViewById(R.id.tvArbli);
bb.setText("a=" + a + " " + b + " " + c + " " + D + " " + x1 + " " + x2);
}
PS You need to do a lot of validation!
Also, always include you logcat (stack trace) for any sort of crash.