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Đặt D = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+..+\frac{1}{100}\)
\(=1-\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{100}\)
\(=1-\frac{1}{100}\)
\(=\frac{99}{100}\)
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\(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+..+\frac{1}{72}=\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{8.9}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-...-\frac{1}{9}\)
\(=\frac{1}{3}-\frac{1}{9}=\frac{2}{9}\)
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Bn ơi 10gam nha bn,bn k cho mk nhé,mk cũng là fan của kudo shinichi nek,mk còn là fan của Sherlock Homels luôn
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D=1/2-1/32=15/32
E=1/1X2+1/2X3+1/3X4+1/4X5+1/5X6
E=1/1-1/6=5/6
K MÌNH NHA
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A)2/3-(1/6+1/8)=2/3-7/24=3/8
B)5/7*14/11*5/7*2/11*5/11*5/7
=5/7*(14/11*2/11*5/11)
=5/7*140/1331=70/1331
C)4/7*(5/4-2/3)*7/8
=4/7*7/12*7/8=1/3*7/8=7/24
Đ)10/1*3+10/3*5+10/5*7+10/7*9+10/9*11
=30/1+50/3+70/5+90/7+110/9
=10+10+10+10+110/9 =40+110/9
=470/9
sao là nhân đúng ko vậy thì
a) 2/3-(1/6+1/8)
=2/3-14/48
=18/48
b)5/7.14/11.5/7.2/11.5/11.5/7
= [ 5/7.5/7.5/7] . [ 2/11.5/11.14/11]
= 125/343 . 140/1331
= 17500/456533 bạn chưa học lũy thừa đúng ko hả con này lấy cả tử cả mẫu nhân với lũy thừa là xong cực nhanh đó
c) 4/7.(5/4-2/3).7/8
=4/7.10/12.7/8
=40/84.7/8
=280/672
d)10/1.3+10/3.5+10/5.7+10/7.9+10/9.11
= 30/1+50/3+70/5+90/7+110/9
=27010/315
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\(\text{Giải:}\)
\(\frac{1}{2}+\frac{3}{4}.\frac{1}{3}=\frac{1}{2}+\frac{3}{12}=\frac{6}{12}+\frac{3}{12}\)\(=\frac{9}{12}\)
\(\frac{2}{3}+\frac{1}{2}-\frac{5}{12}=\frac{8}{12}+\frac{6}{12}-\frac{5}{12}\)\(=\frac{9}{12}\)
\(\text{Học tốt!!!}\)
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1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
= (1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+(10+20)
= 20 + 20 + 20 + 20 + 20 + 20 + 20 + 20 + 20 +30
= 20x9 +30
=180+30
=210
tk cho mik nhé
D=1/2+1/6+1/12+...+1/90+1/100
D=(1/1x2+1/2x3+...+1/9x10)+1/100
D=(1-1/2+1/2-1/3+....+1/9-1/10)+1/100
D=(1-1/10)+1/100
D=9/10+1/100
D=91/100
D=1/2+1/6+1/12+...+1/90+1/100
D=(1/1x2+1/2x3+...+1/9x10)+1/100
D=(1-1/2+1/2-1/3+....+1/9-1/10)+1/100
D=(1-1/10)+1/100
D=9/10+1/100
D=91/100