Source: https://www.coursum3.org/lufr-4-sciences-economiques-mathematiques-et-sociales/?wpdf_download_file=/home/ichigo1vs/www8/wp-content/uploads/cours/UFR4/Administration%20%C3%A9conomique%20et%20sociale%20(AES)/l1/m%C3%A9thode%20de%20travail%20universitaire/TD%201%20MTU.pdf