Đáp án:
Giải thích các bước giải:
6:
a, A = 1+3^2+3^4+...+3^98+3^100
3^2 A =3^2+3^4+3^6+...+3^100+3^102
9A-A =(3^2+3^4+3^6+...+3^100+3^102)-(1+3^2+3^4+...+3^98+3^100)
8A =3^2+3^4+3^6+...+3^100+3^102-1-3^2-3^4-...-3^98-3^100
8A =3^102-1
A = 3^102-1/8
xin loi mik chi biet lam bai 6 thui