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Byju's Answer
Standard XII
Mathematics
Condition for Coplanarity of Four Points
If a , b , ...
Question
If
→
a
,
→
b
,
→
c
are non-coplanar vectors
→
r
.
→
a
=
→
r
.
→
b
=
→
r
.
→
c
=
0
, show that
→
r
is a zero vector.
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Solution
Given
→
r
.
→
a
=
0
;
→
r
.
→
b
=
0
;
→
r
.
→
c
=
0
Let
→
r
is the point of intersection of three planes
→
r
.
→
a
−
→
r
.
→
b
=
0
⇒
→
r
(
→
a
.
→
b
)
=
0...
(
i
)
Similarly
→
r
(
→
a
.
→
c
)
=
0...
(
i
i
)
→
r
⊥
(
→
a
.
→
b
)
;
→
r
⊥
(
→
a
.
→
c
)
∴
→
r
=
k
(
→
a
.
→
b
)
×
(
→
a
.
→
c
)
=
k
(
→
a
×
→
a
−
→
a
×
→
c
−
→
b
×
→
a
+
→
b
×
→
c
)
⇒
→
r
=
k
(
→
a
.
(
→
a
×
→
b
)
+
→
a
.
(
→
b
×
→
c
)
+
→
a
.
(
→
c
×
→
a
)
)
⇒
0
=
k
(
0
+
[
→
a
→
b
→
c
]
)
Suggest Corrections
0
Similar questions
Q.
If
¯
¯
¯
a
,
¯
¯
b
,
¯
¯
c
are non-coplanar vectors, then show that the vectors
−
¯
¯
¯
a
+
3
¯
¯
b
−
5
¯
¯
c
,
−
¯
¯
¯
a
+
¯
¯
b
+
¯
¯
c
and
2
¯
¯
¯
a
−
3
¯
¯
b
+
¯
¯
c
are coplanar
Q.
If
a
,
→
b
,
→
c
→
are three non-coplanar vectors, such that
d
→
·
a
→
=
d
→
·
b
→
=
d
→
·
c
→
=
0
,
then show that
d
→
is the null vector.
Q.
Let
→
a
,
→
b
,
→
c
be three non-coplanar vectors and
→
r
be any vector in space such that
→
r
.
→
a
=
1
,
→
r
.
→
b
=
2
and
→
r
.
→
c
=
3.
If
[
→
a
,
→
b
,
→
c
]
=
1
then
→
r
is equal to
Q.
If
→
a
,
→
b
,
→
c
are three non-coplanar vectors,
→
p
,
→
q
,
→
r
are non-zero vectors such that
→
p
=
→
b
×
→
c
[
→
a
→
b
→
c
]
,
→
q
=
→
c
×
→
a
[
→
a
→
b
→
c
]
,
→
r
=
→
a
×
→
b
[
→
a
→
b
→
c
]
,
then the value of the expression
(
→
a
+
→
b
+
→
c
)
,
(
→
p
+
→
q
+
→
r
)
is
Q.
If
A
,
b
,
c
are three non zero vectors then show that
|
(
a
×
b
)
.
c
|
=
|
a
|
|
b
|
|
c
|
i
f
a
.
b
=
b
.
c
=
c
.
a
=
0
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