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Question : 34 of 160
Marks:
+1 ,
-0
Solution:
It is given that,
a + l b + l 2 c = 0 ∴ ‌ ‌ a × b = l 2 ( b × c ) and
c × a = l ( b × c ) and
‌ ‌ a × b = l ( c × a ) and it is also given that,
‌ ‌ a × b + b × c + c × a = 3 ( b × c ) ⇒ ‌ a × b + c × a = 2 ( b × c ) ⇒ ‌ l 2 ( b × c ) + l ( b × c ) = 2 ( b × c ) ⇒ ‌ l 2 + l − 2 = 0 ⇒ l 2 + 2 l − l − 2 = 0 ⇒ ‌ l ( l + 2 ) − 1 ( l + 2 ) = 0 ⇒ l = − 2 , 1
∴ Minimum value of
l = − 2 © examsiri.com
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