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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
Bài làm
\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}+\frac{1}{110}\)
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}+\frac{1}{10.11}\)
\(A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)
\(A=\frac{1}{1}-\frac{1}{11}\)
\(A=\frac{10}{11}\)
M = \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)
M = \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)
M = 1 -\(\frac{1}{9}\)=\(\frac{8}{9}\)
(dấu . là dấu nhân )
a, \(\frac{3}{2}\cdot\frac{4}{7}+\frac{3}{7}\cdot\frac{3}{2}\)
= \(\frac{3}{2}\left(\frac{4}{7}+\frac{3}{7}\right)\)
=\(\frac{3}{2}\cdot\frac{7}{7}=\frac{3}{2}\)
b, \(\frac{12}{5}\cdot4-4\cdot\frac{7}{5}\)
=\(4\left(\frac{12}{5}-\frac{7}{5}\right)=4\cdot\frac{5}{5}=4\)
c, \(\frac{5}{11}:\frac{1}{2}+\frac{6}{11}:\frac{1}{2}\)
=\(2\left(\frac{5}{11}+\frac{6}{11}\right)=2\cdot\frac{11}{11}=2\)
a;3/2x(4/7+3/7)
=3/2x1
=3/2
b;12/5x4-4x7/5
=4x(12/5-7/5)
=4x1
=4
c;5/11:1/2+6/11:1/2
=1/2:(5/11+6/11)
=1/2:1
=1/2
5/2+13/6+25/12+41/20+61/30+85/42
=2+1/2+2+1/6+2+1/12+2+1/20+2+1/30+2+1/42
=12+(1/2+1/6+1/12+1/20+1/30+1/42)
=12+(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7)
=12+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=12+1-1/7
=90/7
Tính Nhanh
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42
Giải chị tiết hộ mình
Ai nhanh nhất mình cho một tick
\(\frac{1}{2}\)+ \(\frac{1}{6}\)+ \(\frac{1}{12}\)+ \(\frac{1}{20}\)+ \(\frac{1}{30}\)+ \(\frac{1}{42}\)
= \(\frac{6}{7}\)
\(\frac{1}{1\cdot2}\) +\(\frac{1}{2\cdot3}\) +\(\frac{1}{3\cdot4}\) +\(\frac{1}{4\cdot5}\) +\(\frac{1}{5\cdot6}\) +\(\frac{1}{6\cdot7}\) =1-\(\frac{1}{7}\) =\(\frac{6}{7}\)
\(A=\dfrac{2}{6}+\dfrac{2}{12}+\dfrac{2}{20}+\dfrac{2}{30}+...+\dfrac{2}{10100}\)
\(A=2\times\left(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+...+\dfrac{1}{100\times101}\right)\)
\(A=2\times\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{100}-\dfrac{1}{101}\right)\)
\(A=2\times\left(\dfrac{1}{2}-\dfrac{1}{101}\right)\)
\(A=2\times\dfrac{99}{202}\)
\(A=\dfrac{99}{101}\)
1. Giải
Ô tô đi từ Hà nội - hải dương hết số tg là:
8h 30p - 7h 6p = 1h 24p
Đổi 1h 24p = 1,4h
Vận tốc của ô tô là :
56 : 1,4 = 40(km/giờ)
Đ/s:
2.mk ko bít
Làm
2/2 + 2/6 + 2/12 + 2/20 + 2/30 + 2/42
= 2/2 + 2/2.3 + 2/3.4 + 2/4.5 + 2/5.6 + 2/6.7
= 2.( 1/2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 )
= 2. ( 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 )
= 2 . [ ( 1/2 + 1/2 ) + (-1/3 + 1/3 ) + (-1/4 + 1/4 ) + (-1/5 + 1/5 ) + (-1/6 + 1/6 ) - 1/7 ]
= 2 . [ 2/2 - 1/7 ]
= 2 . [ 1 - 1/7 ]
= 2 . [ 7/7 - 1/7 ]
= 2 . 6/7
= 12/7
HỌC TỐT
\(\frac{2}{2}\)+\(\frac{2}{6}\)+\(\frac{2}{12}\)+\(\frac{2}{20}\)+\(\frac{2}{30}\)+\(\frac{2}{42}\)
= \(\frac{2}{1.2}\)+\(\frac{2}{2.3}\)+\(\frac{2}{3.4}\)+\(\frac{2}{4.5}\)+\(\frac{2}{5.6}\)+\(\frac{2}{6.7}\)
= \(\frac{2}{1}\)-\(\frac{2}{2}\)+\(\frac{2}{2}\)-\(\frac{2}{3}\)+\(\frac{2}{3}-\frac{2}{4}\)+\(\frac{2}{4}\)-\(\frac{2}{5}\)+\(\frac{2}{5}\)-\(\frac{2}{6}\)+\(\frac{2}{6}\)-\(\frac{2}{7}\)
=\(\frac{2}{1}\)-\(\frac{2}{7}\)
= \(\frac{12}{7}\)
CỐ GẮNG HOK TỐT NHÉ