NAM GIÀ

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="Giải phương trình bậc 2"
    />
 <EditText
     id="@+id/a"
 	 android:layout_width="300pt" 
     android:layout_height="80pt" 
     android:numeric="true"
 />
 <EditText
     id="@+id/b"
 	 android:layout_width="300pt" 
     android:layout_height="80pt" 
     android:numeric="true"
 />
 <EditText
     id="@+id/c"
 	 android:layout_width="300pt" 
     android:layout_height="80pt" 
     android:numeric="true"
 />
[html:Button
     id="@+id/calculate"
 	 android:layout_width="250pt" 
     android:layout_height="80pt"
      android:text="Calculate"
 /]
<TextView
     id="@+id/result"
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
 />
</LinearLayout>

package com.daohainam.ptb2;

import android.app.Activity;
import android.os.Bundle;
import android.widget.*;
import android.view.*;

public class PTB2 extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);

        final Button button = (Button) findViewById(R.id.calculate);
    	final TextView result = (TextView) findViewById(R.id.result);
        button.setOnClickListener(new Button.OnClickListener() {
            public void onClick(View v) {
            	String sa = ((EditText) findViewById(R.id.a)).getText().toString();
            	String sb = ((EditText) findViewById(R.id.b)).getText().toString();
            	String sc = ((EditText) findViewById(R.id.c)).getText().toString();
            	
            	try
            	{
            		double a = Double.parseDouble(sa);  
            		double b = Double.parseDouble(sb);  
            		double c = Double.parseDouble(sc);
            		
            		if (a == 0)
            		{
            			result.setText("Phương trình bậc I: ");
        				if (b == 0)
        				{
        					if (c == 0)
        						result.setText(result.getText() + "Phương trình có vô số nghiệm");
        					else
        						result.setText(result.getText() + "Phương trình vô nghiệm");
        				}
        				else
        				{
    						result.setText(result.getText() + "x = " + (-c/b));
        				}
            		}
            		else 
            		{
            			double delta = b*b - 4*a*c;
            			
            			if (delta < 0.0)
            			{
            				result.setText("Phương trình vô nghiệm\n");
            			}
            			else
            				if (delta == 0)
            				{
            					result.setText("Phương trình có nghiệm kép = " + (-b/(2*a)));
            				}
            				else
            				{
            					double delta_sqrt = Math.sqrt(delta);
            					result.setText("x1 = " + ((b*b + delta_sqrt)/(2 * a)) + "\n" + "x2 = " + ((b*b - delta_sqrt)/(2 * a)));
            				}
            		}
            			
            	} catch (Exception ex)
            	{
            		result.setText(ex.toString());
            	}
            }
        });
}
}