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Byju's Answer
Standard XII
Mathematics
Applications of Cross Product
For any two v...
Question
For any two vectors
→
a
,
→
b
, prove that
∣
∣
→
a
×
→
b
∣
∣
2
=
∣
∣
∣
→
a
.
→
a
→
a
.
→
b
→
b
.
→
a
→
b
.
→
b
∣
∣
∣
Open in App
Solution
L
.
H
.
S
:
|
→
a
×
→
b
|
2
=
|
→
a
|
2
|
→
b
|
2
sin
2
θ
R
.
H
.
S
:
(
→
a
.
→
a
)
(
→
b
.
→
b
)
−
(
→
a
.
→
b
)
(
→
b
.
→
a
)
=
|
→
a
|
2
|
→
b
|
2
−
(
→
a
.
→
b
)
2
(
∵
→
a
.
→
b
=
→
b
.
→
a
)
=
|
→
a
|
2
|
→
b
|
2
−
(
|
→
a
|
|
→
b
|
cos
θ
)
2
=
|
→
a
|
2
|
→
b
|
2
−
|
→
a
|
2
|
→
b
|
2
cos
2
θ
=
|
→
a
|
2
|
→
b
|
2
(
1
−
cos
2
θ
)
=
|
→
a
|
2
|
→
b
|
2
sin
2
θ
=
L
.
H
S
.
Hence proved.
Suggest Corrections
0
Similar questions
Q.
For any two vectors
^
a
and
^
b
prove that
(a)
|
→
a
+
→
b
|
≤
|
→
a
|
+
|
→
b
|
(b)
|
→
a
−
→
b
|
≤
|
→
a
|
+
|
→
b
|
Q.
Show that
|
→
a
|
→
b
+
|
→
b
|
→
a
is perpendicular to
|
→
a
|
→
b
−
|
→
b
|
→
a
, for any two nonzero vectors
→
a
and
→
b
.
Q.
Show that
|
→
a
|
→
b
+
|
→
b
|
→
a
is perpendicular to
|
→
a
|
→
b
−
|
→
b
|
→
a
for any two nonzero vectors
→
a
and
→
b
Q.
For vectors
→
a
&
→
b
. Prove that
|
→
a
×
→
b
|
2
=
|
→
a
|
2
|
→
b
|
2
−
|
→
a
.
→
b
|
2
Q.
For any three vectors
→
a
,
→
b
and
→
c
, prove that
[
→
a
+
→
b
,
→
b
+
→
c
,
→
c
+
→
a
]
=
2
[
→
a
→
b
→
c
]
. Hence prove that the vectors
→
a
+
→
b
,
→
b
+
→
c
,
→
c
+
→
a
are coplanar. If and only if
→
a
,
→
b
,
→
c
are coplanar.
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