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Byju's Answer
Standard XII
Mathematics
Dot Product of Two Vectors
If a → and b ...
Question
If
a
→
and
b
→
are two non-collinear unit vectors such that
a
→
+
b
→
=
3
,
find
2
a
→
-
5
b
→
·
3
a
→
+
b
→
.
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Solution
We
have
a
→
+
b
→
=
3
Squaring both sides, we get
a
→
+
b
→
2
=
3
⇒
a
→
2
+
b
→
2
+
2
a
→
.
b
→
=
3
⇒
1
+
1
+
2
a
→
.
b
→
=
3
(Because
a
→
and
b
→
are unit vectors)
⇒
2
+
2
a
→
.
b
→
=
3
⇒
2
a
→
.
b
→
=
1
⇒
2
a
→
.
b
→
=
1
⇒
a
→
.
b
→
=
1
2
.
.
.
1
Now,
2
a
→
-
5
b
→
.
3
a
→
+
b
→
=
6
a
→
2
+
2
a
→
.
b
→
-
15
b
→
.
a
→
-
5
b
→
2
=
6
a
→
2
+
2
a
→
.
b
→
-
15
a
→
.
b
→
-
5
b
→
2
(
a
→
.
b
→
=
b
→
.
a
)
→
=
6
a
→
2
-
13
a
→
.
b
→
-
5
b
→
2
=
6
1
-
13
1
2
-
5
1
From (1)
=
1
-
13
2
=
-
11
2
Suggest Corrections
4
Similar questions
Q.
If two vectors
a
→
and
b
→
are such that
a
→
=
2
,
b
→
=
1
and
a
→
·
b
→
=
1
,
then find the value of
3
a
→
-
5
b
→
·
2
a
→
+
7
b
→
.
Q.
Let
→
a
and
→
b
be two vectors such that
|
→
a
|
=
3
,
|
→
b
|
=
6
and
|
→
a
+
→
b
|
=
7
. Then the value of
(
3
→
a
−
2
→
b
)
.
(
2
→
a
+
5
→
b
−
4
→
a
×
→
b
)
is
Q.
If
a
→
and
b
→
are two non-zero non-collinear vectors such that
a
→
×
b
→
=
1
and
a
→
.
b
→
=
3
, then the angle between
a
→
and
b
→
is _____________.
Q.
If
a
and
b
are two non-collinear vectors such that
|
a
|
=
3
,
|
b
|
=
4
and
a
−
b
=
^
i
+
2
^
j
+
3
^
k
, then the value of
{
|
a
−
b
|
|
a
|
|
b
|
}
2
is equal to
Q.
If
→
a
and
→
b
are two non collinear unit vectors and
|
→
a
+
→
b
|
=
√
3
, then
(
2
→
a
−
5
→
b
)
.
(
3
→
a
+
→
b
)
=
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