9^m + 9^m+1 = 20, maka 27^m = ?

9^m + 9^(m + 1) = 20
9^m + 9^m . 9^1 = 20
Misal 9^m = a => a = 3^(2m) = (3^m)^2
a + a . 9 = 20
10a = 20
a = 2
(3^m)^2 = 2
3^m = √2

27^m = 3^3m = (3^m)^3 = √2 . √2 . √2 = 2√2