Đáp án+Giải thích các bước giải:
A)
P = 1 + 5 + 25 + ....... 78125
5xP=5+25+125+625+...+390625
5xP-P=390625-1
4xP=390624
P=390624:4
P=97656
Vậy P=97656
B)
Q = 2+8+32+.......+32768
2Q = 4+16+64+.........+65536
2Q-Q= ( 4+16+64+.........+65536 ) - ( 2+8+32+.......+32768 )
Q = 65536 - 2
C)
H = 1 + $\frac{1}{5}$ + $\frac{1}{25}$ + ............ + $\frac{1}{15625}$
5H = 5 + 1 + $\frac{1}{5}$ + $\frac{1}{25}$ + ............ + $\frac{1}{3125}$
5H - H = ( 5 + 1 + $\frac{1}{5}$ + $\frac{1}{25}$ + ............ + $\frac{1}{3125}$ ) - ( 1 + $\frac{1}{5}$ + $\frac{1}{25}$ + ............ + $\frac{1}{15625}$ )
4H = 5 - $\frac{1}{15625}$
4H = $\frac{78124}{15625}$
H = $\frac{78124}{15625}$:4
H = $\frac{78124}{62500}$
