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Question : 30 of 160
Marks:
+1,
-0
Solution:
Given,
|a|=|b|=2,a.b=2 and
a+b+c=0, then
|c|= ?
a+b+c=0 ⇒
|a+b+c|2=0 ⇒|a|2+|b|2+|c|2+2(a.b+b.c+c.a)=0
22+22+|c|2+2[2+c(a+b)]=0 ⇒
4+4+|c|2+2[2+c(−c)]=0 { from Eq. (i),
a+b=−c} ⇒
8+|c|2+4−2|c||2=0 ⇒
|c|2=12⇒|c|=2√3
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