2х² - 13х + 21 = 0
D = b² - 4ac = (-13)² - 4 · 2 · 21 = 169 - 168 = 1
√D = √1 = 1
х₁ = (13-1)/(2·2) = 12/4 = 3
х₂ = (13+1)/(2·2) = 14/4 = 7/2 = 3 целых 1/2 = 3,5
ответ: (3; 3,5).
