1/7+1/91+1/247+1/475+1/775+1/1147=? (1)
ta có: (1) <=>: 1/(1.7)+1/(7.13)+1/(13.19)+1/(19.25)+1/(25.31)+1/(31.37)
=1/6.(1-1/7+1/7-1/13+1/13-1/19+1/19-1/25+1/25-1/31+1/31-1/37)
=1/6.(1-1/37)=6/37
a= 1/1.7+4/7.13+4/13,19+4/19.25 +...+4/43.49
1/1.7+1/7.13+1/13.19+......+1/61.67
1/1.2.3+1/2.3.4+1/3.4.5+.......+1/8.9.10
1/1+2 + 1/1+2+3 + 1/1+2+3+4 +.......+ 1/1+2+3+....+99
CẦN GẤP
a, A=1.7+7.13+13.19+19.25+.....+9.97
b, B= 2^2+3^2+4^2+...........+80^2
c, C=1.99+2.98+3.97+.......+99.1
giúp mình đc ko
mình đang cần gấp
Tính bằng cách hợp lí :
\(A=1.7+7.13+13.19+....+91.97\)
5/1.7+5/7.13+5/13.19+...+5/2017.2023
36/1.7 + 36/7.13+36/13.19+...+36/94.100
Tính : S = 4/1.7 + 4/7.13 + 4/ 13.19 + 4/43.49
Tìm x biết
5/1.7+5/7.13+5/13.19+...+5/x.(x+6)=10075/12096
tìm x
\(X:\left(\frac{5}{1.7}+\frac{5}{7.13}+\frac{5}{13.19}+...+\frac{5}{601.607}\right)=0\)
