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Byju's Answer
Standard XII
Mathematics
Applications of Dot Product
For vectors ...
Question
For vectors
→
a
&
→
b
. Prove that
|
→
a
×
→
b
|
2
=
|
→
a
|
2
|
→
b
|
2
−
|
→
a
.
→
b
|
2
Open in App
Solution
We know that,
∣
∣
→
a
×
→
b
∣
∣
2
=
|
→
a
|
2
∣
∣
→
b
∣
∣
2
sin
2
θ
∣
∣
→
a
×
→
b
∣
∣
2
=
|
→
a
|
2
∣
∣
→
b
∣
∣
2
(
1
−
cos
2
θ
)
∣
∣
→
a
×
→
b
∣
∣
2
=
|
→
a
|
2
∣
∣
→
b
∣
∣
2
−
|
→
a
|
2
∣
∣
→
b
∣
∣
2
cos
2
θ
-------------------(1)
We have,
∣
∣
→
a
.
→
b
∣
∣
2
=
|
→
a
|
2
∣
∣
→
b
∣
∣
2
cos
2
θ
Substitute in (1)
∴
∣
∣
→
a
×
→
b
∣
∣
2
=
|
→
a
|
2
∣
∣
→
b
∣
∣
2
−
∣
∣
→
a
.
→
b
∣
∣
2
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0
Similar questions
Q.
For any two vectors
→
a
,
→
b
, prove that
∣
∣
→
a
×
→
b
∣
∣
2
=
∣
∣
∣
→
a
.
→
a
→
a
.
→
b
→
b
.
→
a
→
b
.
→
b
∣
∣
∣
Q.
Let
→
a
and
→
b
be two unit vectors. the maximum value of
∣
∣
→
a
+
→
b
∣
∣
2
−
∣
∣
→
a
−
→
b
∣
∣
2
∣
∣
→
a
+
→
b
∣
∣
2
+
∣
∣
→
a
−
→
b
∣
∣
2
is equal to
Q.
Prove that
[
→
a
+
→
b
,
→
b
+
→
c
,
→
c
+
→
a
]
=
2
[
→
a
,
→
b
,
→
c
]
Q.
I : If
|
→
a
+
→
b
|
=
|
→
a
−
→
b
|
, then
(
→
a
,
→
b
)
=
π
2
.
II : If
→
a
,
→
b
,
→
a
+
→
b
are unit vectors, then
(
→
a
,
→
b
)
=
2
π
3
.
Q.
If
→
a
,
→
b
,
→
c
are three vectors and
→
a
+
→
b
+
→
c
=
0
prove that
→
a
×
→
b
=
→
b
×
→
c
=
→
c
×
→
a
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