Formules, vergelijkingen https://www.youtube.com/watch?v=LMSnzZdmDjk
Vergelijkingen, bordjes leggen https://www.youtube.com/watch?v=1HMD9yiYrEc
A x B = 0 https://www.youtube.com/watch?v=C3ylRGNm7Qs
Wat is de balansmethode? https://www.youtube.com/watch?v=jE2zC2oQMWM&list=RDCMUCw_N3obzNBAbDXV0pSrr_xA&start_radio=1&rv=jE2zC2oQMWM&t=19
Balancemethode 2 https://www.youtube.com/watch?v=kkk0QqLo1tI&list=RDCMUCw_N3obzNBAbDXV0pSrr_xA&index=2