A=3i+4j+k, b=i-2j+7k, c=3i-6j+2k a) 5a, 2b, c b) 4b, 2c c)

a)  5a = 5(3; 4; 1) = (15; 20; 5);

     2b = 2(1; -2 ; 7) = (2; -4; 14);

     c = (3; -6; 2).

b) 4b = 4(1; -2; 7) = (4; -8; 28);

    2c = 2(3; -6; 2) = (6; -12; 4).

c) a = (3; 4; 1);

    c = (3; -6; 2).

d) 2a = 2(3; 4; 1) = (6; 8; 2);

    3b = 3(1; -2; 7) = (3; -6; 21);

    c = (3; -6; 2).