`S = 1+3^2+3^4+....+3^98+3^100`
`9S = 3^2+3^4+....+3^100+3^102`
`9S-S=(3^2+3^4+....+3^100+3^102)-(1+3^2+....+3^98+3^100)`
`8S=3^102-1`
`S = (3^102-1)/8`
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`S = 3^2+3^4+....+3^98+3^100`
`9S =3^4+3^5+....+3^98+3^102`
`9S-S=(3^2+3^4+....+3^98+3^102)-(3^2+3^4+....+3^98+3^100)`
`8S=3^102-3^2`
`S=(3^102-3^2)/8`
XIN HAY NHẤT Ạ!