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# Given 3 vectors: A = 4k B = 8i + k C = 3i - 4j then C(A • B) =_______?

The answer should be 13 but the way I'm doing it must be wrong because gives me another number. Please show your work so I can see what I'm missing. Thanks :)

### 2 Answers

- ?Lv 78 years agoFavorite Answer
A = 4k = 0i + 0j + 4k

B = 8i + k = 8i + 0j + k

C = 3i - 4j = 3i - 4j + 0k

Now, (A • B) = (0*8 + 0*0 + 4*1) = 4 --- a scalar quantity

C(A • B) = (3i - 4j + 0k)*4 = (12i - 16j + 0k) = (12i - 16j) ---- a vector quantity

If you want the magnitude of C(A • B)

it is given by | C(A • B) | = | (12i - 16j) | = √(12² + 16²) = 20

How the answer is 13, I am also not able to understand.

If your question is something else write it as it is without modifying.

- gaddLv 44 years ago
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