NIMCET 2018 — Mathematics PYQ
NIMCET | Mathematics | 2018The vector a=αi^+2j^+βk^ lies in the plane of the vector b=i^+j^ and c=j^+k^ and bisects the angle between b and c. Then, which one of the following gives possible values of α and β?
Choose the correct answer:
- A.
α=2,β=2
- B.
α=1,β=2
- C.
α=2,β=1
α=1,β=1
Explanation
Concept:
If two or more vectors lie on the same plane than they are called coplanar vector and satisfies the conditions
</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">aamp;bamp;c</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">=0
</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">ax</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">bx</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">cxamp;ayamp;byamp;cyamp;azamp;bzamp;cz</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">=0
Calculation:
aamp;bamp;c=0
<br>α10amp;2amp;1amp;1amp;βamp;0amp;1=0
α+β=2
Also, a bisects the angle between b and c.
<br>a=2λ(b^+c^)
=2λ(i^+2j^+k^)
On comparing with a=αi^+2j^+βk^,
We get, λ=2, α=1, and β=1
Explanation
Concept:
If two or more vectors lie on the same plane than they are called coplanar vector and satisfies the conditions
</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">aamp;bamp;c</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">=0
</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">ax</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">bx</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">cxamp;ayamp;byamp;cyamp;azamp;bzamp;cz</span><br><spanstyle="font−size:14pt;font−family:arial,helvetica,sans−serif;">=0
Calculation:
aamp;bamp;c=0
<br>α10amp;2amp;1amp;1amp;βamp;0amp;1=0
α+β=2
Also, a bisects the angle between b and c.
<br>a=2λ(b^+c^)
=2λ(i^+2j^+k^)
On comparing with a=αi^+2j^+βk^,
We get, λ=2, α=1, and β=1

