so sanh 1/15+1/16+1/17+1/18+......+1/30 voi 1/2
S = 1/4 + 1/16 + 1/17 + 1/18 + 1/61 + 1/62 + 1/63. So sanh S voi 1/2
Cho S = 1/11 + 1/12 + 1/13 + 1/14 + 1/15 + 1/16 + 1/17 + 1/18 + 1/19 + 1/20.
Hay so sanh S va 1/2
Cho S=1/11+1/12+1/13+1/14+1/15+1/16+1/17+1/18+1/19+1/20
HÃY SO SÁNH S VOI 1/2
cho S=1\3+1\5+1\18+1\30+1\45+1\60+...+1\1485 so sanh S voi 3\5
Cho S = 1/11+1/12+1/13+1/14+115+1/16+1/17+1/18+1/19+1/20
hãy so sanh S và 1/2
so sanh
10 ^15+1 phần 10^16+1 va 10^16+1 phan 10^17+1
Đặt \(A=\frac{10^{15}+1}{10^{16}+1}\Rightarrow10A=\frac{10^{16}+10}{10^{16}+1}=1+\frac{9}{10^{16}+1}\)
Đặt \(B=\frac{10^{16}+1}{10^{17}+1}\Rightarrow10B=\frac{10^{17}+10}{10^{17}+1}=1+\frac{9}{10^{17}+1}\)
Vì \(10^{16}+1< 10^{17}+1\Rightarrow\frac{9}{10^{16}+1}>\frac{9}{10^{17}+1}\)
\(\Rightarrow10A>10B\Rightarrow A>B\)
\(\Rightarrow\frac{10^{15}+1}{10^{16}+1}>\frac{10^{16}+1}{10^{17}+1}\)
so sanh:1/2+1/4+1/8+1/16+............+1/512 voi 1
A=(1/4-1).(1/9-1).(1/16-1)......(1/400-1) . so sanh A voi -1/2
so sanh S=1/30+1/31+1/32+....+1/59+1/60 voi 1/2
S=1/30+1/31+1/32+1/33+...+1/59+1/60
S có 31 phân số,ta thấy:
1/30>1/62 1/31>1/62 1/32>1/62 ............ 1/60>1/62
Vậy:
S>31.1/62
S>31/62
S>1/2
Vậy S>1/2
Chúc em học tốt^^