Answer:
see explanation
Step-by-step explanation:
c = a - 2b
= < 4, 5, 6 > - 2 < 1, 2, 3 > ← multiply each component by 2
= < 4, 5, 6 > - < 2, 4, 6 > ← subtract corresponding components
= < 4 - 2, 5 - 4, 6 - 6 > = < 2, 1, 0 >
| c | = =
=
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sum the product of corresponding components
u.v = (3 × 2) + (- 2 × - 1) + (4 × - 6) = 6 + 2 - 24 = - 16