service.html

<div ng-app="app" ng-controller="controller">
  <div>
    <input type="number" ng-model="number" />
    <button ng-click="square()">
      Square
    </button>
  </div>
  <div>
    Result: {{result}}
  </div>
</div>

service.js

var app = angular.module('app',[]);

app.factory('MathFactory',function(){
	var factory = {};
  factory.add = function(a,b){
  	return a + b;
  }
  
  factory.subtraction = function(a,b){
  	return a - b;
  }
  
  factory.multiply = function(a,b){
  	return a * b;
  }
  
  return factory;
  
})

app.service('Calc',function(MathFactory){
  this.square = function(a){
  	return MathFactory.multiply(a,a);
  }
});

app.controller('controller',function($scope,Calc){
	$scope.result = 2;
  $scope.square = function(){
  	$scope.result = Calc.square($scope.result)
  }
})