a) \(\dfrac{2}{1.2.3}+\dfrac{2}{2.3.4}+\dfrac{2}{3.4.5}+...+\dfrac{2}{18.19.20}\)
b) \(\dfrac{4}{1.3.5}+\dfrac{4}{3.5.7}+\dfrac{4}{5.7.9}+...+\dfrac{4}{21.23.25}\)
c) \(\dfrac{3}{1.2}-\dfrac{5}{2.3}+\dfrac{7}{3.4}-\dfrac{9}{4.5}+...+\dfrac{39}{19.20}-\dfrac{41}{20.21}\)
d) \(\dfrac{8}{9}\cdot\dfrac{15}{16}\cdot\dfrac{24}{25}\cdot...\cdot\dfrac{99}{100}\cdot\dfrac{120}{121}\)
e) \(\left(1+\dfrac{7}{9}\right)\left(1+\dfrac{7}{20}\right)\left(1+\dfrac{7}{33}\right)\left(1+\dfrac{7}{48}\right)...\left(1+\dfrac{7}{180}\right)\)
Các bạn không nhất thiết phải làm hết, làm cho nó dễ hiểu được thì càng tốt để mk vận dụng
1. Chứng minh rằng:
a) A = 1/ 1.2.3 + 1/2.3.4 + 1/3.4.5 + .... + 1/ 18.19.20 < 1/4
b ) B = 36/1.2.3 + 36/3.5.7 + .... + 36/25.27.29 < 3
Giúp mình nha , cảm ơn nhiều lắm !!
Chứng minh rằng :
a) A=\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{18.19.20}<\frac{1}{4}\)
b) B=\(\frac{36}{1.3.5}+\frac{36}{3.5.7}+\frac{36}{5.7.9}+...+\frac{36}{25.27.29}<3\)
c/m 1/1.2.3 + 1/2.3.4 + 1/3.4.5 +.......+ 1/18.19.20 < 1/4
B=1/1.2.3+1/2.3.4+.....+1/18.19.20. Chứng minh B<1/4
Chứng minh rằng: 1/1.2.3+1/2.3.4+1/34.5+.....+1/18.19.20<1/4
Tính giá trị biểu thức:
a) A = -11/23.10/-13 +-11/13.3/-23-2/23
b) B = 1/1.2.3 + 1/2.3.4 + ... + 1/18.19.20
c) C = 52/1.6 + 52/6.11 + 52/11.16 +...+ 52/31.35
d) D = 1. 2 .3 + 2 .4. 6+ 4 .8 .12 + 7 .14 .21/ 1. 3. 5 + 2. 6. 10 + 4 .12 .20 + 7 .21 .35 + 3/5
GIÚP MIK VS AK!
Chứng minh:
A=1/1.2.3+1/2.3.4+1/3.4.5+...+1/18.19.20 < 1/4
S = 1/1.2.3 + 1/2.3.4 + ... + 1/18.19.20.
chung to : S < 1/4