Installing Nova 2.0 on Laravel 5.8 is throwing errors

I followed the guide from Nova documentation. after adding the required lines into composer.json I tried to run composer update and this is what I get:

Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - laravel/nova 2.0.x-dev requires moontoast/math ^1.1 -> satisfiable by moontoast/math[1.1.0, 1.1.1, 1.1.2].
    - laravel/nova dev-master requires moontoast/math ^1.1 -> satisfiable by moontoast/math[1.1.0, 1.1.1, 1.1.2].
    - moontoast/math 1.1.2 requires ext-bcmath * -> the requested PHP extension bcmath is missing from your system.
    - moontoast/math 1.1.1 requires ext-bcmath * -> the requested PHP extension bcmath is missing from your system.
    - moontoast/math 1.1.0 requires ext-bcmath * -> the requested PHP extension bcmath is missing from your system.
    - Installation request for laravel/nova * -> satisfiable by laravel/nova[2.0.x-dev, dev-master].

  To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php/7.2/cli/php.ini
    - /etc/php/7.2/cli/conf.d/10-mysqlnd.ini
    - /etc/php/7.2/cli/conf.d/10-opcache.ini
    - /etc/php/7.2/cli/conf.d/10-pdo.ini
    - /etc/php/7.2/cli/conf.d/15-xml.ini
    - /etc/php/7.2/cli/conf.d/20-bz2.ini
    - /etc/php/7.2/cli/conf.d/20-calendar.ini
    - /etc/php/7.2/cli/conf.d/20-ctype.ini
    - /etc/php/7.2/cli/conf.d/20-curl.ini
    - /etc/php/7.2/cli/conf.d/20-dom.ini
    - /etc/php/7.2/cli/conf.d/20-exif.ini
    - /etc/php/7.2/cli/conf.d/20-fileinfo.ini
    - /etc/php/7.2/cli/conf.d/20-ftp.ini
    - /etc/php/7.2/cli/conf.d/20-gd.ini
    - /etc/php/7.2/cli/conf.d/20-gettext.ini
    - /etc/php/7.2/cli/conf.d/20-iconv.ini
    - /etc/php/7.2/cli/conf.d/20-json.ini
    - /etc/php/7.2/cli/conf.d/20-mbstring.ini
    - /etc/php/7.2/cli/conf.d/20-mysqli.ini
    - /etc/php/7.2/cli/conf.d/20-pdo_mysql.ini
    - /etc/php/7.2/cli/conf.d/20-phar.ini
    - /etc/php/7.2/cli/conf.d/20-posix.ini
    - /etc/php/7.2/cli/conf.d/20-readline.ini
    - /etc/php/7.2/cli/conf.d/20-shmop.ini
    - /etc/php/7.2/cli/conf.d/20-simplexml.ini
    - /etc/php/7.2/cli/conf.d/20-sockets.ini
    - /etc/php/7.2/cli/conf.d/20-sysvmsg.ini
    - /etc/php/7.2/cli/conf.d/20-sysvsem.ini
    - /etc/php/7.2/cli/conf.d/20-sysvshm.ini
    - /etc/php/7.2/cli/conf.d/20-tokenizer.ini
    - /etc/php/7.2/cli/conf.d/20-wddx.ini
    - /etc/php/7.2/cli/conf.d/20-xmlreader.ini
    - /etc/php/7.2/cli/conf.d/20-xmlwriter.ini
    - /etc/php/7.2/cli/conf.d/20-xsl.ini
    - /etc/php/7.2/cli/conf.d/20-zip.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.

any help is appreciated in advance.