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Byju's Answer
Standard XII
Mathematics
Applications of Dot Product
Prove that ...
Question
Prove that
(
→
a
+
→
b
)
⋅
(
→
a
+
→
b
)
=
|
→
a
|
2
+
∣
∣
→
b
∣
∣
2
if and only if
→
a
→
b
are perpendicular, given
→
a
≠
→
0
,
→
b
≠
→
0
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Solution
To prove :
(
→
a
+
→
b
)
(
→
a
+
→
b
)
=
|
→
a
|
2
+
|
→
b
|
2
Given,
→
a
and
→
b
are perpendicular
Proof since
→
a
and
→
b
are perpendicular
therefore the dot product formula
→
a
.
→
b
=
|
→
a
|
|
→
b
|
cos
90
o
[
cos
90
o
=
0
]
→
a
.
→
b
=
0
Now,
L
H
S
=
(
→
a
+
→
b
)
.
(
→
a
+
→
b
)
=
→
a
.
→
a
+
→
a
.
→
b
+
→
b
.
→
a
+
→
b
.
→
b
=
→
a
.
→
a
+
→
b
.
→
b
[
→
a
.
→
b
=
→
b
.
→
a
=
0
]
|
→
a
|
2
+
|
→
b
|
2
[
→
a
.
→
a
=
|
→
a
|
2
]
=
R
H
S
Hence proved
Suggest Corrections
0
Similar questions
Q.
→
a
≠
→
0
,
→
b
≠
→
0
,
→
a
×
→
b
=
→
0
,
→
c
×
→
b
=
→
0
⇒
→
a
×
→
c
=
Q.
If
|
→
a
|
=
2
,
∣
∣
→
b
∣
∣
=
3
and
→
a
,
→
b
are mutually perpendicular, then the area of the triangle whose vertices are
→
0
,
→
a
+
→
b
,
→
a
−
→
b
is
Q.
If
→
a
+
→
b
+
→
c
=
→
0
show that
→
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 unit vectors such that
→
a
+
→
b
+
→
c
=
→
0
and
(
→
a
,
→
b
)
=
π
3
, then
∣
∣
→
a
×
→
b
∣
∣
+
∣
∣
→
b
×
→
c
∣
∣
+
|
→
c
×
→
a
|
=
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