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Let a1, a22, a322, , a1029 be a G.P. of common ratio 1 2. If a1 + a2 + + a10 = 62, then a1 is equal to:
(2) 2( 2 - 1)
ak2k - 1 = a1 ( 1 2 )k - 1
ak = a1 2k - 1( 2)k - 1 = a1( 2)k - 1
a1, a2, , a10 is a G.P. with common ratio 2
a1 + a2 + + a10 = a1 ( 2)10 - 1 2 - 1 = 31a1 2 - 1
31a1 2 - 1 = 62
a1 = 2( 2 - 1)
Answer: (2)
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