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Byju's Answer
Standard VI
Mathematics
Perimeter of a Triangle
If the vector...
Question
If the vectors
→
α
=
a
ˆ
i
+
a
ˆ
j
+
c
ˆ
k
,
→
β
=
ˆ
i
+
ˆ
k
,
γ
=
c
ˆ
i
+
c
ˆ
j
+
b
ˆ
k
are coplanar, then prove that c is the geometric mean of a and b.
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Solution
Since
→
α
,
→
β
,
→
γ
are coplanar vectors.
Therefore,
[
→
α
→
β
→
γ
]
=
0
∣
∣ ∣
∣
a
a
c
1
0
1
c
c
b
∣
∣ ∣
∣
=
0
a
(
0
−
c
)
−
a
(
b
−
c
)
+
c
(
c
−
0
)
=
0
−
a
c
−
a
b
+
a
c
+
c
2
=
0
c
2
=
a
b
Therefore, c is the geometric mean of a and b.
Hence Proved
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Similar questions
Q.
If vectors
a
¯
i
+
a
¯
j
+
c
¯
¯
¯
k
,
¯
i
+
¯
¯
¯
k
,
c
¯
i
+
c
¯
j
+
b
¯
¯
¯
k
are coplanar, then
C
is
Q.
Let
a
,
b
and
c
be distinct non-negative numbers. If vectors
a
ˆ
i
+
a
ˆ
j
+
c
ˆ
k
,
ˆ
i
+
ˆ
k
and
c
ˆ
i
+
c
ˆ
j
+
b
ˆ
k
are coplanar, then
c
is
Q.
Let a, b, c be distinct non-negative numbers. If the vectors
a
i
+
a
j
+
c
k
+
,
i
+
k
and
c
i
+
c
j
+
b
k
lie in a plane, then c is
Q.
Let
a
,
b
and
c
be distinct non-negative numbers. If the vectors
a
i
+
a
j
+
c
k
,
i
+
k
and
c
i
+
c
j
+
b
k
lie in a plane, then
c
is
Q.
Statement-
1
:
→
l
=
a
¯
i
+
b
¯
j
+
c
¯
¯
¯
k
,
→
m
=
b
¯
i
+
c
¯
j
+
a
¯
¯
¯
k
,
→
n
=
c
¯
i
+
a
¯
j
+
b
¯
¯
¯
k
are coplanar (where
a
,
b
,
c
are positive) then
a
=
b
=
c
.
Statement-
2
: If
l
→
a
+
m
→
b
+
n
→
c
=
→
0
such that
l
,
m
,
n
not all zero then
→
a
,
→
b
→
c
are coplanar.
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