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2 tháng 4 2019

1 + 2 + 3 +...+ 50

Dãy trên có số số hạng là:

\(\left(50-1\right)+1=50\) (số)

Tổng của chúng là:

\(\frac{\left(50+1\right)\cdot50}{2}=1275\)

Vậy tổng của chúng là 1275

~Học tốt~

27 tháng 11 2021

\(\dfrac{8}{9}+\dfrac{3}{18}=\dfrac{16}{18}+\dfrac{3}{18}=\dfrac{19}{18}\)          \(\dfrac{5}{7}-\dfrac{4}{11}=\dfrac{55}{77}-\dfrac{28}{77}=\dfrac{3}{11}\)

 

\(\dfrac{3}{4}+\dfrac{4}{5}=\dfrac{15}{20}+\dfrac{16}{20}=\dfrac{21}{20}\)            \(\dfrac{5}{7}-\dfrac{3}{5}=\dfrac{25}{35}-\dfrac{21}{35}=\dfrac{4}{35}\)

 

\(\dfrac{7}{9}X\dfrac{3}{4}=\dfrac{7}{9}X\dfrac{3}{4}=\dfrac{7}{12}\)                    \(\dfrac{8}{3}X\dfrac{21}{4}=\dfrac{8}{3}X\dfrac{21}{4}=14\)

 

\(\dfrac{12}{7}:\dfrac{1}{4}=\dfrac{12}{7}X\dfrac{4}{1}=\dfrac{48}{7}\)                 \(\dfrac{7}{2}:\dfrac{9}{4}=\dfrac{7}{2}X\dfrac{4}{9}=\dfrac{14}{9}\)

a: =5/7+1/6

=30/35+7/35

=37/35

b: =5/8+3/4

=5/8+6/8

=11/8

c: =10/12+9/12

=19/12

d: =9/24+14/24

=23/24

26 tháng 2 2023

câu a sai anh ạ

1 tháng 1 2022

Câu 10:

\(a,y\times7+y\times3=70\\ \Rightarrow y\times\left(7+3\right)=70\\ \Rightarrow y\times10=70\\ \Rightarrow y=7\\ b,18:y+12:y=3\\ \Rightarrow\left(18+12\right):y=3\\ \Rightarrow30:y=3\\ \Rightarrow y=10\)

câu 11:

\(a,9\times365+2\times365-365=\left(9+2-1\right)\times365=10\times365=3650\\ b,108:9-18:9=\left(108-18\right):9=90:9=10\\ c,43\times95+4\times43+43=43\times\left(95+4+1\right)=43\times100=4300\)

24 tháng 2 2022

\(\dfrac{12}{6}+\dfrac{15}{7}=2+\dfrac{15}{7}=\dfrac{14}{7}+\dfrac{15}{7}=\dfrac{29}{7}\\ \dfrac{12}{13}-\dfrac{8}{9}=\dfrac{108}{117}-\dfrac{104}{117}=\dfrac{4}{117}\\ \dfrac{43}{54}+\dfrac{76}{8}=\dfrac{43}{54}+\dfrac{19}{2}=\dfrac{43}{54}+\dfrac{513}{54}=\dfrac{556}{54}=\dfrac{278}{27}\)

24 tháng 2 2022

\(\dfrac{12}{6}+\dfrac{15}{7}=\dfrac{84}{42}+\dfrac{90}{42}=\dfrac{174}{42}=\dfrac{29}{7}\)

\(\dfrac{12}{13}-\dfrac{8}{9}=\dfrac{108}{117}-\dfrac{104}{117}=\dfrac{4}{117}\)

\(\dfrac{43}{54}+\dfrac{76}{8}=\dfrac{344}{432}+\dfrac{4104}{432}=\dfrac{4448}{432}=\dfrac{278}{27}\)

8 tháng 5 2023

\(1,\\ c,\dfrac{17}{6}-\dfrac{3}{7}-\dfrac{5}{6}=\dfrac{17\times7-3\times6-5\times7}{6\times7}=\dfrac{119-18-35}{42}=\dfrac{66}{42}=\dfrac{11}{7}\\ 2,\\ a,\dfrac{6}{9}+\dfrac{3}{15}+\dfrac{7}{15}\\ =\dfrac{6:3}{9:3}+\dfrac{7+3}{15}\\ =\dfrac{2}{3}+\dfrac{10}{15}\\ =\dfrac{2}{3}+\dfrac{2}{3}\\ =\dfrac{2+2}{3}=\dfrac{4}{3}\)

\(b,\dfrac{7}{2}+\dfrac{29}{12}-\dfrac{11}{12}\\ =\dfrac{7}{2}+\left(\dfrac{29}{12}-\dfrac{11}{12}\right)\\ =\dfrac{7}{2}+\dfrac{29-11}{12}\\ =\dfrac{7}{2}+\dfrac{18}{12}\\ =\dfrac{7}{2}+\dfrac{18:6}{12:6}\\ =\dfrac{7}{2}+\dfrac{3}{2}\\ =\dfrac{7+3}{2}=\dfrac{10}{2}=5\)

\(c,\dfrac{26}{25}-\dfrac{3}{5}-\dfrac{2}{5}\\ =\dfrac{26}{25}-\dfrac{3\times5}{5\times5}-\dfrac{2\times5}{5\times5}\\ =\dfrac{26-15-10}{25}\\ =\dfrac{1}{25}\)

8 tháng 5 2023

Bài 1:
\(\dfrac{17}{6}-\dfrac{3}{7}-\dfrac{5}{6}=\left(\dfrac{17}{6}-\dfrac{5}{6}\right)-\dfrac{3}{7}=2-\dfrac{3}{7}=\dfrac{14}{7}-\dfrac{3}{7}=\dfrac{11}{7}\)
Bài 2:
a/\(\dfrac{6}{9}+\dfrac{3}{15}+\dfrac{7}{15}\)
\(=\dfrac{2}{3}+\left(\dfrac{3}{15}+\dfrac{7}{15}\right)\)
\(=\dfrac{2}{3}+\dfrac{2}{3}\)
\(=\dfrac{4}{3}\)
b/\(\dfrac{7}{2}+\dfrac{29}{12}-\dfrac{11}{12}\)
\(=\dfrac{7}{2}+\left(\dfrac{29}{12}-\dfrac{11}{12}\right)\)
\(=\dfrac{7}{2}+\dfrac{3}{2}\)
\(=5\)
c/\(\dfrac{26}{25}-\dfrac{3}{5}-\dfrac{2}{5}\)
\(=\dfrac{26}{25}-\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\)
\(=\dfrac{26}{25}-1\)
\(=\dfrac{26}{25}-\dfrac{25}{25}\)
\(=\dfrac{1}{25}\)
#Đang Bận Thở

\(=\dfrac{11}{12}\left(\dfrac{2}{7}+\dfrac{4}{7}+\dfrac{1}{7}\right)=\dfrac{11}{12}\cdot1=\dfrac{11}{12}\)

18 tháng 2 2022

=11/12