After installing lapack via:
yum install lapack lapack-devel
and restarting httpd service I still get
Fatal error: Class 'Lapack' not found in /var/www/html/metody_obliczeniowe/proj1/3.php on line 135
when trying to use the example from: http://php.net/manual/en/lapack.solvelinearequation.php
You need to install the lapack extension.
# pecl install lapack