If bar(a) is a unit vector perpendicular to bar(b) and (bar(a)+2bar(b))*(3bar(a)-bar(b))=-9 then |bar(b)|= bigcirc sqrt(12) bigcirc sqrt(6) bigcirc sqrt(6) bigcirc sqrt(5)
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1
Answer:
Correct option is
B
∣
a
ˉ
∣=
2
∣
b
ˉ
∣
(
a
+
b
).
b
=0and(
a
+2
b
).
a
=0
⇒
a
.
b
+
∣
∣
∣
∣
b
∣
∣
∣
∣
2
=0⇒∣
a
∣
2
+2
b
.
a
=0
a
.
b
=−
∣
∣
∣
∣
2
⇒∣
a
∣=
2
∣
∣
∣
∣
b
∣
∣
∣
∣
.
Hence,theoptionBiscorrectanswer.
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