Question

please write the answer.​

Answer 1

$Use, A.B = |A| |B| cos \theta$

Explanation:

$Given, \: \: A = 2i + j + 2k \: \: and \: \: B = 2i - 2 j - k \\ Now, \: \: \: A.B \: = (2i + j + 2k).(2i - 2 j - k) \\ = 2 \times 2 + 1 \times - 2 + 2 \times - 1 \\ = 4 - 2 - 2 = 0 \\ Then, \: \: A.B = |A| |B| cos \theta = 0 \\ cos \theta = 0 \\ \theta = \frac{\pi}{2} \\ so \: \: \: A \: \: and \: \: B \: \: are \: \: perpendicular$