Thấy 1/41+1/42 +......+ 1/60 < 1/40 .20
1/41 +1/42 + .....+1/60<1/2
mà 1/61 +1/62+......+1/80 < 1/60 .20 =1/3
suy ra 1/41+1/42+ .......+1/80 <1/2 +1/3=7/12(đpcm)
Lại có 1/41 +1/42 +.....+1/80 <1/40 .40 =1(đpcm)
Thấy 1/41+1/42 +......+ 1/60 < 1/40 .20
1/41 +1/42 + .....+1/60<1/2
mà 1/61 +1/62+......+1/80 < 1/60 .20 =1/3
suy ra 1/41+1/42+ .......+1/80 <1/2 +1/3=7/12(đpcm)
Lại có 1/41 +1/42 +.....+1/80 <1/40 .40 =1(đpcm)
Hãy chứng tỏ rằng
\(\frac{7}{12}< \frac{1}{41}+\frac{1}{42}+...+\frac{1}{79}+\frac{1}{80}< 1\)\(1\)
Điền dấu ( > ; < ; = ) vào chỗ trống
\(\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+.....+\frac{1}{79}+\frac{1}{80}\) \(.........\) \(\frac{5}{6}\)
khó quá nghĩ mãi không ra
Chứng tỏ rằng : 7/12 <1/41 +1/42 + 1/43 + 1/44 + ..... +1/79 +1/80 <1
Chứng tỏ rằng :
A=\(\frac{1}{2}-\frac{1}{4}+\frac{1}{8}-\frac{1}{16}+\frac{1}{32}-\frac{1}{64}\) < \(\frac{1}{3}\)
B=\(\frac{1}{5}+\frac{1}{9}+\frac{1}{10}+\frac{1}{41}+\frac{1}{42}< \frac{1}{2}\)
Please help me if you know!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I need answer!!!!!!!!!!!!!!!!!!
Chứng minh rằng \(\frac{1}{3}+\frac{1}{7}+\frac{1}{13}+\frac{1}{21}+\frac{1}{31}+\frac{1}{43}+\frac{1}{57}+\frac{1}{73}+\frac{1}{91}< 1\)
Cho tổng A=\(\frac{1}{10}+\frac{1}{11}+\frac{1}{12}+...\frac{1}{99}+\frac{1}{100}\)
Chứng tỏ rằng A > 1
Chứng minh rằng : \(\frac{1}{3}+\frac{1}{7}+\frac{1}{13}+\frac{1}{21}+\frac{1}{31}+\frac{4}{43}+\frac{1}{57}+\frac{1}{73}+\frac{1}{91}<1\)
( lời giải chi tiết nha , mình đang cần gấp )
Chứng minh:7/12< 1/41+1/42+1/43+...+1/79+1/80<1
Cho A=\(\frac{1}{101}\)+\(\frac{1}{102}\)+\(\frac{1}{103}\)+ . . . . . . . .+\(\frac{1}{199}\)+\(\frac{1}{200}\)
a)chứng tỏ rằng A<\(\frac{3}{4}\)(tách 2 dòng)
chứng tỏ rằng A >\(\frac{7}{12}\)(tách 2 dòng)
chứng tỏ rằng A >\(\frac{5}{8}\)(tách 4 dòng)