First slide

Vectors

Question

If a vector 2i+3i+8k is perpendicular to the vector 4 i -4j + $α$ k, then the value of $α$ is

Moderate

A

1 /2
B

-1 /2
C

1
D

-1

Solution

For two vectors to be perpendicular
$A \cdot B = 0$
$\begin{array}{lc} ∴ (2 i + 3 j + 8 k) \cdot (4 j - 4 i + αk) = 0 \\ or - 8 + 12 + 8 α = 0 \\ \begin{array}{c} or 8 α = - 4 or α = - \frac{1}{2} \end{array} \end{array}$

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