Answer:
2i²+5ij+3ik-12j²-10jk-2k²
Explanation:
a=2i-3j-k
b=i+4j+2k
ab = (2i-3j-k) (i+4j+2k)
Multiply both bracket by expanding the bracket
2i(i+4j+2k)-3j(i+4j+2k)-k(i+4j+2k)
Multiply
2i²+8ij+4ik-3ij-12j²-6jk-ik-4jk-2k²
Collect like terms
2i²+8ij-3ij+4ik-ik-12j²-6jk-4jk-2k²
2i²+5ij+3ik-12j²-10jk-2k²