So sánh C= 3+3^2+3^3 +...+3^100
Giải thích
C=3+32+33+...+3100
3C=3.3+32.3+33.3+...+3100.3
3C=32+33+34+...+3101
3C−C=32+33+34+...+3101−3+32+33+...+3100
2C=32+33+34+...+3101−3−32−33−...−3100
2C=3101−3
C=3101−32
Vậy C=D
C=3+32+33+...+3100
3C=3.3+32.3+33.3+...+3100.3
3C=32+33+34+...+3101
3C−C=32+33+34+...+3101−3+32+33+...+3100
2C=32+33+34+...+3101−3−32−33−...−3100
2C=3101−3
C=3101−32
Vậy C=D