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Question : 40 of 120
Marks:
+1,
-0
Solution:
|a|=3,|b|=4,|c|=5a+b+c=0⟹a+b=−c⇒|a+b|=|−c|⇒|a+b|2=|−c|2⇒|a|2+|b|2+2a⋅b=|c|2⇒9+25+2a⋅b=49Also
ab=3×5Hence
9+25+2ab‌cos‌θ=49⇒15=30‌cos‌θOr
cos‌θ=‌θ=60∘so angle is
60∘.
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