第13章 13.3

(1)

$a + b = (1,2,3) + (2,3,1) = (3,5,4)$

(2)

$a + b + c = (1,2,3) + (2,3,1) + (3,1,2) = (6,6,6)$

(3)

$a + 2b - 3c = (1,2,3) + 2(2,3,1) - 3(3,1,2) = (-4,5,-1)$