CM: 1/2+1/3+1/4+...+1/15 < 3
1 cm S=1+2+2^2+...+2^39 chia hết cho 15
2 cm A=a+a^2+a^3+ ...+a^2.n chia hết cho a+1
3 cm tổng 3 số tự nhiên liên tiếp chia hết cho 3
,...... 5.................................................5
4 cho a, b thuộc N và a- b chia hết cho 7. cm 4.a +3.b chia hết cho 7
Cm
a) 1/5+1/13+1/14+1/15+1/61+1/62+1/63 nhỏ hơn 1/2
b) 1/2 +1/2^2 +1/2^3 +....+1/2^20 nhỏ hơn 1
c) 1/4+1/5+1/6+...+1/19 lớn hơn 1
d) 3/1.4+3/4.7 +3/7.10 +...+3/40.43+3/43.46 nhỏ hơn 1
e) 1/2^2 + 1/3^2 +1/4^2 +1/5^2 +1/6^2+1/7^2+1/8^2 nhỏ hơn 1
Cho \(S=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{15^2}\)
\(CM:\frac{7}{16}< S< \frac{14}{15}\)
(5/7-7/7)-[0,2-(-2/7-1/10]
(3-1/4+2/3)-(5-1/3-5/6)-(6-7/4+-3/2)
1/3-3/4--3/5+1/64-2/9-1/3+1/15
3/5:(1/15-1/6)+3/5:(-1/3-16/15)
1/2(-3/4-13/14):5/7-(-2/21+1/7):7/7
chứng minh
a) (a+a^2+a^3+a^4+................+a^29+a^30) chia hết (a+1)
b)15/460+15/498+15/754+.............+15/6160<1
c)1/2-1/4+1/8-1/16++1/32-1/64<1/3
d)1/3-2/3^2+3/3^3-4/3^4+...........+99/3^99+100/3^100
giúp mk vs nha
C=1/2^2+1/3^2+1/4^2+...+1/19^2+1/20^2
CM C <3/4
D=1/2^2+1/3^2+1/4^2+...+1/100^2
CM D<1
Tính :
C= 1/5+1/10+1/20+1/40+...+1/1280D= 2/1*3+2/3*5+2/5*10+2/7*9+2/9*11+2/11*18+2/13*15E= 4/3*7+4/7*11+4/11*15+4/15*19+4/19*23+4/23*27G= 1/2+1/6+1/12+1/20+1/30+1/42+...+1/110H= 3/1*2+3/2*3+3/3*4+3/4*5+...+3/9*10Giúp mk nha *.*
tính nhanh
a,(-3/4 + 5/13):2/7-(2/1/2+8/13):2/7
b,-3/5:(-1/15-1/6)+3/5:(-1/3-1/1/15)
c,(3-1/4+2/3)-(5-1/3-6/5)-(6-7/4+3/2)
