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Byju's Answer
Standard XII
Mathematics
Dot Product
Prove that po...
Question
Prove that points
A
,
B
,
C
having positions vectors
→
a
,
→
b
,
→
c
are collinear, if
[
→
b
×
→
c
+
→
c
×
→
a
+
→
a
×
→
b
]
=
→
0
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Solution
If A,B,C are collinear,
¯
A
B
and
¯
B
C
are parallel.
⇒
¯
A
B
×
¯
B
C
=
0
(
¯
b
−
¯
a
)
×
(
¯
c
−
¯
b
)
=
0
¯
b
×
¯
c
−
¯
b
×
¯
b
−
¯
a
×
¯
c
+
¯
a
×
¯
b
=
0
But,
¯
b
×
¯
b
=
0
¯
b
×
¯
c
−
¯
a
¯
c
+
¯
a
×
¯
b
=
0
¯
b
×
¯
c
+
¯
c
×
¯
a
+
¯
a
×
¯
b
=
0
∵
(
¯
a
×
¯
b
)
=
−
¯
b
×
¯
a
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0
Similar questions
Q.
If
→
a
,
→
b
,
→
c
are unit vectors such that
→
a
+
→
b
+
→
c
=
→
0
and
(
→
a
,
→
b
)
=
π
3
then
|
→
a
×
→
b
|
+
|
→
b
×
→
c
|
+
|
→
c
×
→
a
|
=
Q.
If
→
a
,
→
b
,
→
c
are unit vectors such that
→
a
+
→
b
+
→
c
=
→
0
and
(
→
a
,
→
b
)
=
π
3
, then
∣
∣
→
a
×
→
b
∣
∣
+
∣
∣
→
b
×
→
c
∣
∣
+
|
→
c
×
→
a
|
=
Q.
If
→
a
,
→
b
,
→
c
are three vectors such that
→
a
×
→
b
=
→
c
,
→
b
×
→
c
=
→
a
,
→
c
×
→
a
=
→
b
then prove that
|
→
a
|
=
|
→
b
|
=
|
→
c
|
Q.
If
→
a
,
→
b
,
→
c
are positive vectors of vertices
A
,
B
,
C
of
Δ
A
B
C
. If
→
r
is position vector of a point
P
such that
(
|
→
b
−
→
c
|
+
|
→
c
−
→
a
|
+
|
→
a
−
→
b
|
)
→
r
=
|
→
b
−
→
c
|
→
a
+
|
→
c
−
→
a
|
→
b
+
∣
∣
→
a
−
→
b
∣
∣
→
c
then the point
P
always
Q.
If
→
a
,
→
b
,
→
c
are non-zero non-collinear vectors such that
→
a
×
→
b
=
→
b
×
→
c
=
→
c
×
→
a
, then
→
a
+
→
b
+
→
c
=
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