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\(\frac{19}{28};\frac{80}{79};\frac{112}{111};\frac{2013}{2012}\)
\(\frac{99}{100};\frac{61}{62};\frac{43}{45};\frac{15}{17}\)
\(A=11+14+17+...+62+65\)
Số số hạng của \(A\)là
\(\left(65-11\right)\div3+1=19\)(số hạng)
Tổng của \(A\)là:
\(\left(11+65\right)\times19\div2=722\)
Đáp số: 722
\(B=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\)
\(B=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\)
\(B=\left(\frac{3-1}{1.3}+\frac{5-3}{3.5}+.....+\frac{9-7}{7.9}+\frac{11-9}{9.11}\right)\times\frac{1}{2}\)
\(B=\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.....+\frac{1}{9}-\frac{1}{11}\right)\times\frac{1}{2}\)
\(B=\left(1-\frac{1}{11}\right)\times\frac{1}{2}\)
\(B=\frac{10}{11}\times\frac{1}{2}\)
\(B=\frac{5}{11}\)
\(C=\frac{3}{10}+\frac{3}{40}+\frac{3}{88}+\frac{3}{154}\)
\(C=\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}\)
\(C=\left(\frac{3}{2}-\frac{3}{5}+\frac{3}{5}-\frac{3}{8}+....+\frac{3}{11}-\frac{3}{14}\right)\div3\)
\(C=\left(\frac{3}{2}-\frac{3}{14}\right)\div3\)
\(C=\frac{9}{7}\div3\)
\(C=\frac{3}{7}\)
\(B=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\)
\(B=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\)
\(B=1-\frac{1}{11}\)
\(B=\frac{10}{11}\)
\(\dfrac{15}{35}=\dfrac{15:5}{35:5}=\dfrac{3}{7}\)
\(\dfrac{24}{27}=\dfrac{24:3}{27:3}=\dfrac{8}{9}\)
\(\dfrac{17}{50}\) ( phân số dã tối giản )
\(\dfrac{15}{45}=\dfrac{15:3}{45:3}=\dfrac{5}{15}=\dfrac{5:5}{15:5}=\dfrac{1}{3}\)
\(\dfrac{99}{121}=\dfrac{99:11}{121:11}=\dfrac{9}{11}\)
`24/27` chưa được rút gọn nha:'>
\(\dfrac{24}{27}=\dfrac{24:3}{27:3}=\dfrac{8}{9}\)
A = \(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+...+\frac{1}{129.15}\)
A = \(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+...+\frac{1}{129.15}\)
A = \(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{129}-\frac{1}{15}\)
A = \(\frac{1}{3}-\frac{1}{15}\)= \(\frac{5}{15}-\frac{1}{15}\)
A = \(\frac{4}{15}\)
CẢM ƠN LỜI GỢI Ý
Ta có:
\(\frac{42}{43}=\frac{43-1}{43}=1-\frac{1}{43}\)
\(\frac{17}{18}=\frac{18-1}{18}=1-\frac{1}{18}\)
\(\frac{14}{15}=\frac{15-1}{15}=1-\frac{1}{15}\)
\(\frac{26}{27}=\frac{27-1}{27}=1-\frac{1}{27}\)
\(\frac{32}{33}=\frac{33-1}{33}=1-\frac{1}{33}\)
Vì \(\frac{1}{15}>\frac{1}{18}>\frac{1}{27}>\frac{1}{33}>\frac{1}{43}\)
=>\(1-\frac{1}{15}
học lớp 5 nhưng mình lười học toán ắm nên chịu nha
chắc C