code: public function getSlope($dp = 0)
      {
          if ($dp != 0) {
              $coefficients = [];
              foreach ($this->slope as $coefficient) {
                  $coefficients[] = round($coefficient, $dp);
              }
  
              return $coefficients;
          }
  
          return $this->slope;
      }
docs: Return the Slope of the line.
  
  @param int $dp Number of places of decimal precision to display
  
  @return string