© examsiri.com
Question : 89 of 160
Marks:
+1,
-0
Solution:
Let
S=1+‌+‌+‌+...On comparing with
(1+x)n=1+nx+‌x2+...,we get
nx=‌ . . . (i)
and
‌‌‌x2=‌ . . . (ii)
From (i) and (ii)
‌=‌ ⇒‌‌=‌⇒2n−2=5n⇒n=−‌On Putting the value of
n in Eq. (i), we get
−‌x=‌ ⇒‌‌x=−‌ ∴S=(1+x)n=(1−‌)−2∕3=(‌)−2∕3=‌3√16
© examsiri.com
Go to Question: