Нужна помощь в решении задачи

function Vector(arr) { 
   this.arr = arr; 
} 
 
Vector.prototype = { 
 
    add: function(v){ 
            if(this.arr.length != v.length){ 
                throw new Error('Size mismatch'); 
            } 
            var add_res = []; 
            for(var i = 0; i < this.arr.length; i++){ 
                add_res.push(this.arr[i] +v[i]); 
            } 
            return add_res; 
    }, 
 
    subtract: function(v){ 
            if(this.arr.length != v.length){ 
                throw new Error('Size mismatch'); 
            } 
            var subtract_res = []; 
            for(var i = 0; i < this.arr.length; i++){ 
                subtract_res.push(this.arr[i] - v[i]); 
            } 
            return subtract_res; 
    }, 
 
    dot: function(v){ 
        if(this.arr.length != v.length){ 
                throw new Error('Size mismatch'); 
            } 
            var dot_res = 0; 
            for(var i = 0; i < this.arr.length; i++){ 
                dot_res += (this.arr[i] *= v[i]); 
            } 
            return dot_res; 
    }, 
 
    norm: function(v){ 
        var res = 0; 
        for(var i = 0; i < this.arr.length; i++){ 
            res += Math.pow(this.arr[i], 2); 
        }    
        return Math.sqrt(res);      
    }, 
    equals: function(v){ 
        if(this.toString() == v.toString()){ 
            return true; 
        } 
        return false; 
    }, 
    toString: function () { 
        return '(' + this.arr.join(',') + ')'; 
    }, 
}