B = 1/22 + 1/32 + 1/42 + 1/52 + 1/62 + 1/72 + 1/82 < 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8
B = < 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8
B = < 1 - 1/8 < 1
=> đpcm
chung to rang B=1/2^2+1/3^2+1/4^2+1/5^2+1/6^2+1/7^2+1/8^2<1
ai lam duoc minh tick cho
chung to rang B= 1/22 + 1/32+1/42+1/52 +1/62 +1/72 +1/82 <1
1) Thuc hien phep tinh:
a) 4^6 × 9^2 / 6^3 × 8^2
b) 5^6 × 15^4 /5^4 × 3^3
c) 3^9 - 2^3 × 3^7 + 2^10 × 3^2 - 2^13 / 3^10 - 2^2 × 3^7 + 2^10 × 3^3 - 2^12
d) (1/9)^10 : (1/3)^20
e) (1/64)^5 × (1/4)^7
2) Chung minh rang:
a)2014^100+2014^99 chia het cho 2015
b) 4^13+32^5-8^8 chia het cho 5
c) 81^27-27^9-9^13 chia het cho 405
Help me!! Pleass!!
Cho B=1/5+1/6+1/7+...+1/17 .Chung to rang B<2
Chứng tỏ rằng: 1/3^2+1/4^2+1/5^2+...+1/60^2<4/9
Cho A=1/3^2+1/4^2+1/5^2+...+1/50^2
Chung to rang a,A>1=4 b,A>4/9
a)chung minh A= 2^1+2^2+2^3+2^4+...2^2010chia het cho 3
b)chung minh B= 3^1+3^2+3^3+3^4+...3^2010chia het cho 4
c)chung minh C= 5^1+5^2+5^3+5^4+...5^2010chia het cho 6
d)chung minh D= 7^1+7^2+7^3+7^4+...7^2010chia het cho 8
Chung to rang
1/32 + 1/42 + 1/52 + 1/62 + ...+ 1/102 <1/2
Cho A=1/3^2+1/4^2+1/5^2+...+1/50^2
Chung to rang a,A>1=4 b,A>4/9
