Tip:A–D to answerE for explanationV for videoS to reveal answer
The least positive integral value of α, for which the angle between the vectors a^i^−2j^+2k^ and αi^+2a^j^−2k^ is acute, is
- A.
1
- B.
2
- C.
5
(Correct Answer) - D.
4
Explanation
Since, the angle is acute
∴cosθ⩾0
⇒(α2−4α−41⩾0)
⇒(α−2)2⩾8
⇒∣α−2∣⩾22
∴α∈(−∞,−22+2)∪[2+22;∞)
∴ Least value of α=5
Explanation
Since, the angle is acute
∴cosθ⩾0
⇒(α2−4α−41⩾0)
⇒(α−2)2⩾8
⇒∣α−2∣⩾22
∴α∈(−∞,−22+2)∪[2+22;∞)
∴ Least value of α=5