Questions about prototypes and inheritance processing on nodes.

TypeError: obj3.sayHello1 is not a function
    at Object.<anonymous> (C:\Users\DEV05\Desktop\nodejs\workspace\hello_basic\h
ello_inherit.js:50:6)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Function.Module.runMain (module.js:441:10)
    at startup (node.js:134:18)
    at node.js:962:3

var util = require('util');

//define Parent Class
var Parent = function(){
  this.sayHello1 = function(){
      console.log('1 :: Parent Origin :: sayHello1()');
  };
};
Parent.prototype.sayHello2 = function(){
    console.log('2 :: Parent Prototype :: sayHello2()');
}

//define Child Class
var Child = function(){
    this.sayHello3 = function(){
      console.log('3 :: Child Origin :: sayHello3()');
  };
};
Child.prototype.sayHello4 = function(){
    console.log('4 :: Child Prototype :: sayHello4()');
}

//use Parent's Function by Parent
var obj1 = new Parent();
console.log('============================================');
console.log('[log] obj1 :: ', obj1);
obj1.sayHello1();
obj1.sayHello2();

//use Parent's Function by Child
var obj2 = new Child();
console.log('============================================');
console.log('[log] obj2 :: ', obj2);
obj2.sayHello3();
obj2.sayHello4();

//apply inherits
util.inherits(Child, Parent);
console.log('============================================');
console.log('[log] Parent :: ', Parent);
console.log('[log] Child :: ', Child);
console.log('[log] Parent.prototype :: ', Parent.prototype);
console.log('[log] Child.prototype :: ', Child.prototype);


//show inherited Child
var obj3 = new Child();
console.log('============================================');
console.log('[log] apply inherits Parent() to Child() ');
obj3.sayHello1();  //error
obj3.sayHello2();  //error