code: function(n) {
              var sum = new Frac(0), l=this.coeffs.length;
              for(var i=0; i<l; i++) {
                  var t = this.coeffs[i];
                  if(!t.equals(0)) sum = sum.add(t.multiply(new Frac(Math.pow(n, i))));
              }
              return sum;
          }
docs: Substitutes in a number n into the polynomial p(n)
  @param {Number} n
  @returns {Frac}