\(S=\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+\dfrac{2}{7\times9}+\dfrac{2}{9\times11}\)
\(=\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\)
\(=\dfrac{1}{1}-\dfrac{1}{11}=\dfrac{11}{11}-\dfrac{1}{11}=\dfrac{10}{11}\)
( 1/1.3+1/3.5+1/5.7+1/7.9+1/9.11). X = 2/3
2^2/1.3+2^2/3.5+2^2/5.7+2^2/7.9+2^2/9.11
lam dc se dc like
Tính tổng 4/1.3+4/3.5+4/5.7+4/7.9+4/9.11+.....+4/2013.2015
Tính:
a) M=2/3.5+2/5.7+2/7.9+...+2/97.99
b) N=3/5.7+3/7.9+3/9.11+...+3/197.199
\(\dfrac{2}{3.5}+\dfrac{2}{5.7}\dfrac{2}{7.9}+.........+\dfrac{2}{99.101}\)
\(P=\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}+\dfrac{2}{11.13}+\dfrac{2}{13.15}\)
Tính :
1/1.3 + 1/3.5 + 1/5.7 + 1/7.9 + 1/9.11 !!
MK bt Đ/S ra 5/11 nhưng cần cách giải đúng !!
TÍNH
Q = \(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\)
a, tính a= 2/1.3+2/3.5+2/5.7+2/7.9+...+2/2017.2019
b, cho S= 1/31+1/32+1/33...+1/60. chứng minh S<4/5
chú ý / là phần
tính
a) 2/3.5+2/5.7+2/7.9+2/9.11+2/11.13
b) 1/1.2.3.4+1/2.3.4.5+1/3.4.5.6+1/27.28.29.30
