Дано: a= 2 j - 3 j + k ; b = - j + 4 j - k . Найти скалярное произведение ( a+ b ) * (2a - b)

a+b = (2i -3j +k) + (-i +4j - k) = i + j
2a - b = (4i - 6j + 2k) - (-i + 4j - k) = 5i -10j + 3k
(a +b)*(2a-b) = (i+j)(5i - 10j + 3k) =
= [5(i)^2 - 10ij + 3kj] +[5ij - 10(j)^2 + 3kj} =
=[5*1 - 10*0 +3*0] + [5*0 -10*1 + 3*0] =
= 5 - 10 = -5