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Byju's Answer
Standard XII
Mathematics
Vector Triple Product
Find λ when t...
Question
Find λ when the projection of
a
→
=
λ
i
^
+
j
^
+
4
k
^
on
b
→
=
2
i
^
+
6
j
^
+
3
k
^
is 4 units.
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Solution
We have
a
=
λ
i
^
+
j
^
+
4
k
^
and
b
=
2
i
^
+
6
j
^
+
3
k
^
The projection of
a
→
on
b
→
is
a
→
.
b
→
b
→
Given that
a
→
.
b
→
b
→
=
4
⇒
λ
i
^
+
j
^
+
4
k
^
.
2
i
^
+
6
j
^
+
3
k
^
2
i
^
+
6
j
^
+
3
k
^
⇒
2
λ
+
6
+
12
4
+
36
+
9
=
4
⇒
2
λ
+
18
7
=
4
⇒
2
λ
+
18
=
28
⇒
2
λ
=
10
∴
λ
=
5
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