Question

4 - 2 + 1 -1/2 +...........1/64=.....
a. 6.156/512
b. 3078/512
c. 1539/512
d. 513/512

Answer 1

4 - 2 + 1 - 1/2 + .... + 1/64 = ....
a = 4, r = -2/4 = -1/2
Un = ar^(n-1)
=> 1/64 = 4(-1/2)^(n - 1)
=> 1/64 . 1/4 = (-1/2)^(n - 1)
=> 1/256 = (-1/2)^(n - 1)
=> (-1/2)^8 = (-1/2)^(n - 1)
=> 8 = n - 1
=> 9 = n
S9 = a(1 - r^9)/(1 - r)
= 4(1 - (-1/2)^9) / (1 - (-1/2))
= 4(1 - (-1/512)) / (1 + 1/2)
= 4(513/512) / (3/2)
= 4 . 513/512 . 2/3
= 1368/512
tak ada di option sy dptnya