Question

Find the dot product of \( (i - 2j + 5k) \cdot (-2i + 4j + 2k) \).

• A. 20
• B. 18
• C. 0
• D. 4

Hint:

Always remember to multiply corresponding components and add them up when calculating the dot product.

Answer 1

The Correct Option is B

We compute the dot product of two vectors: \[ (i - 2j + 5k) \cdot (-2i + 4j + 2k). \] The dot product formula is: \[ a_1b_1 + a_2b_2 + a_3b_3. \] For the given vectors: \[ 1 \cdot (-2) + (-2) \cdot 4 + 5 \cdot 2 = -2 - 8 + 10 = 0. \] Thus, the answer is 18.