Question

If and are two mutually perpendicular vectors, where = and = $2 \vec { i } + 2 \hat { j } - a \hat { k }$ , then the value of a is

• A. −2
• B. 8
• C. −7
• D. −8

Answer 1

Answer: (B)

8

Answer 2

$\overrightarrow { \mathrm { A } }$ ⊥

$\overrightarrow { \mathrm { A } }$ . = 0 = ()( $2 \vec { i } + 2 \hat { j } - a \hat { k }$ )

= 10 + 14 − 3a

∴ 3a = 24 ⇒ a = 8

Hence (2) is correct.