Đặt A =4/1x3 + 6/3x6+8/6x10 +14/10x17 +12/17x23 . => A/2 = 2/1x3 +3/3x6 +4/6x10+7/10x17 +6/17x23. =>A/2 = 1-1/3 + 1/3-1/6+1/6-1/10+1/10-1/17+1/17-1/23. => A/2=1-1/23 . => A/2=22/23 . => A=44/23 . cho mik nha

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\(A=\frac{4}{1.3}+\frac{6}{3.6}+\frac{8}{6.10}+\frac{14}{10.17}+\frac{12}{17.23}\)

\(=2\left(\frac{2}{1.3}+\frac{3}{3.6}+\frac{4}{6.10}+\frac{7}{10.17}+\frac{6}{17.23}\right)\)

\(=2\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+\frac{1}{10}-\frac{1}{17}+\frac{1}{17}-\frac{1}{23}\right)\)

\(=2\left(1-\frac{1}{23}\right)\)

\(=2\cdot\frac{22}{23}=\frac{44}{23}\)

\(2.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right).y=\frac{2}{3}\)

\(2\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)

\(2.\left(\frac{1}{1}-\frac{1}{11}\right).y=\frac{2}{3}\)

\(2.\frac{10}{11}.y=\frac{2}{3}\)

\(\frac{20}{11}.y=\frac{2}{3}\)

\(\Rightarrow y=\frac{11}{30}\)

Study well 

Ta có : \(\widehat{O_1}\)và \(\widehat{O_3}\) (  đối đỉnh )

\(\widehat{O_1}\)   và \(\widehat{O_3}=130^o\left(gt\right)\)

\(\Rightarrow\widehat{O_1}=\widehat{O_3}=\frac{130^o}{2}=65^o\)

\(\widehat{O_2}=\widehat{O_4}=180^o-65^o=115^o\)

Chúc bạn học tốt !!!

\(\frac{x}{6}+\frac{x}{10}+\frac{x}{15}+\frac{x}{21}+\frac{x}{28}+\frac{x}{39}=\frac{8}{9}.\)

\(\Rightarrow x.\left(\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{39}\right)=\frac{8}{9}\)

\(\Rightarrow x.\frac{23}{52}=\frac{8}{9}\)

\(\Rightarrow x=\frac{426}{207}\)

Study well 

\(\frac{x}{6}+\frac{x}{10}+\frac{x}{15}+\frac{x}{21}+\frac{x}{28}+\frac{x}{39}=\frac{8}{9}\)

<=> x\(\left(\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{x}{39}\right)=\frac{8}{9}\)

<=> x = \(\frac{8}{9}:\frac{23}{52}\)

<=> x = \(\frac{416}{207}\)

(1-1/2).(1.1/3).(1.1-4)....(1-1/2016)

=1/2.2/3.3/4.4/5....2015/2016

=1.2.3....2015/2.3.4....2016

=1/2016

1/2016

Hmm...-1 ?!

theo mk là số: -1

\(=\frac{4}{8}+\frac{6}{8}-\frac{1}{8}\)

\(=\frac{9}{8}\)

học tốt

\(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}\)

\(=\frac{4}{8}+\frac{2}{8}+\frac{1}{8}\)

\(=\frac{7}{8}\)

Study well 

a,Chiều dài là:

60.4/3=80(m)

Diện tích khu vườn là:

80.60=4800(m2)

b,Diện tích trông cây ăn quả là:

4800.7/12=2800(m2)

Diện tích còn lại là:

4800-2800=2000(m2)

Diện tích đào ao là:

2000.30%=600(m2)

Đáp số : a,4800m2      b,600m2

Cảm ơn bạn nhiều lắm ! 

\(\left|2x-1\right|-5=\frac{3}{4}\)

\(=>\left|2x-1\right|=\frac{23}{4}\)

\(=>2x-1=\pm\frac{23}{4}\)

\(\hept{\begin{cases}2x-1=\frac{23}{4}=>x=\frac{27}{8}\\2x-1=-\frac{23}{4}=>x=-\frac{19}{8}\end{cases}}\)

\(\frac{2}{3}\cdot x+\frac{3}{7}=-\frac{1}{2}\)

\(=>\frac{2}{3}\cdot x=-\frac{1}{14}\)

\(=>x=-\frac{3}{28}\)