Răspuns:
Daca a si b sunt direct proportionale inseamna ca:
(1/3)/20 = (2/3)/40 = (3/4)/45 = (4/5)/48
(1/3)/20 = (2/3)/40 <=> 20 * 2/3 = 40 * 1/3 <=> 40/3 = 40/3
(1/3)/20 = (3/4)/45 <=> 20 * 3/4 = 45 * 1/3 <=> 60/4 = 45 / 3 <=> 15=15
(1/3)/20 = (4/5)/48 <=> 20 * 4/5 = 48 * 1/3 <=> 80/5 = 48/4 <=> 16 = 12 (fals) =>
=> Marimile a si b NU sunt direct proportionale