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Byju's Answer
Standard XII
Mathematics
Applications of Dot Product
a.i i+ a.j j+...
Question
(
a
.
i
)
i
+
(
a
.
j
)
j
+
(
a
.
k
)
k
=
A
0
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B
a
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C
3
a
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D
None of these
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Solution
The correct option is
A
a
Let
a
=
x
i
+
y
j
+
z
k
Now,
(
a
.
i
)
i
+
(
a
.
j
)
j
+
(
a
.
k
)
k
=
[
(
x
i
+
y
j
+
z
k
)
.
i
]
i
+
[
(
x
i
+
y
j
+
z
k
)
.
j
]
j
+
[
(
x
i
+
y
j
+
z
k
)
.
k
]
k
=
x
i
+
y
j
+
z
k
=
a
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0
Similar questions
Q.
Assertion :If
i
×
[
(
a
−
j
)
×
i
]
+
j
×
[
(
a
−
k
)
×
j
]
+
k
[
(
a
−
i
)
×
k
]
=
0
, then
a
=
1
2
(
i
+
j
+
k
)
. Reason:
(
a
.
i
)
i
+
(
a
.
j
)
j
+
(
a
.
k
)
k
=
a
for any vector
a
.
Q.
The roots of the quadratic equation
(
a
+
b
)
x
2
−
3
b
x
−
3
a
=
0
∀
a
,
b
∈
R
are
Q.
(
a
2
-
b
2
)
3
+
(
b
2
-
c
2
)
3
+
(
c
2
-
a
2
)
3
(
a
-
b
)
3
+
(
b
-
c
)
3
+
(
c
-
a
)
3
=
(a) 3(a + b) ( b+ c) (c + a)
(b) 3(a − b) (b − c) (c − a)
(c) (a − b) (b − c) (c − a)
(d) none of these