Edit in JSFiddle

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

app.service('MathService', function() {
    this.add = function(a, b) { return a + b };
    
    this.subtract = function(a, b) { return a - b };
    
    this.multiply = function(a, b) { return a * b };
    
    this.divide = function(a, b) { return a / b };
});

app.service('CalculatorService', function(MathService){
    
    this.square = function(a) { return MathService.multiply(a,a); };
    this.cube = function(a) { return MathService.multiply(a, MathService.multiply(a,a)); };

});

app.controller('CalculatorController', function($scope, CalculatorService) {

    $scope.doSquare = function() {
        $scope.answer = CalculatorService.square($scope.number);
    }

    $scope.doCube = function() {
        $scope.answer = CalculatorService.cube($scope.number);
    }
});
<div ng-app="app">
    <div ng-controller="CalculatorController">
        Enter a number:
        <input type="number" ng-model="number" />
        <button ng-click="doSquare()">X<sup>2</sup></button>
        <button ng-click="doCube()">X<sup>3</sup></button>
        
        <div>Answer: {{answer}}</div>
    </div>
</div>
body {
    font-family:sans-serif;
    background-color: #f5f5f5;
}
div {
    margin:20px 5px;
}