Evaluate if a = 6.
a + a? =

Step-by-step explanation:

if a=6

a+a=12

cause 6×2=12

:)

364/27

Step-by-step explanation:

9, 3, 1, ... is a geometric sequence with common ratio r = 1/3.

The nth term is a1rn-1.

If a1rn-1 = 1/27, then 9(1/3)n-1 = 1/27

                                32(3-1)n-1 = 3-3

                                3231-n = 3-3

                                    33-n = 3-3

                                      3-n = -3

                                         n = 6

The sum, Sn, of the first n terms of a geometric sequence is given by Sn = a1(1 - rn) / (1 - r).

So, 9 + 3 + 1 + ... + 1/27 = S6 = 9(1 - (1/3)6) / (1 - 1/3)

                                              = 9(1 - 1/729) / (2/3)

                                              = (27/2)(728/729) = 364/27