Question

cho t =3+3^2+...+3^99 tim so tu nhien n biet rang 2t+3=3^2n

 

Answer 1

3t=3^2+3^3+..+3^100

=>3t-t=(3^2+3^3+..+3^100)-(3+3^2+...+3^99)

=>2t=3^100-3

=>2t+3=3^100-3+3=3^100=(3^2)^50

 Mà 2t+3=3^2n=(3^2)^n

=>n=50

vậy n=50

Answer 2

t =3+3^2+...+3^99

=>3t=3^2+3^3+3^4+..+3^100

=>3t-t=(3^2+3^3+3^4+...+3^100)-(3+3^2+..+3^99)

=>2t=3^100-3

=>2t+3=3^100

=>3^2n=3^100

=>2n=100=>n=50