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CBSE Class 12 Math 2012 Solved Paper

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Question : 4
Total: 29
Find 'λ' when the projection of
→
a
 = λ
^
i
+
^
j
+4
^
k
 on
→
b
 = 2
^
i
+6
^
j
+3
^
k
 is 4 units
Solution:  
Projection of
→
a
 on
→
b
 =
→
a
.
→
b
|
→
b
|
 = 4 (given)
⇒
(λ
^
i
+
^
j
+4
^
k
).(2
^
i
+6
^
j
+3
^
k
)
√22+62+32
= 4
⇒
2λ+6+12
7
 = 4
⇒ λ = 5
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