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Nhiều thế :( Làm 1,2 câu thôi nhé
a) \(\frac{1}{3}+\frac{1}{4}=\frac{4}{12}+\frac{3}{12}=\frac{7}{12}\) (bị mất nét nhưng vẫn nhìn ra là số 12 nhỉ?)
b) \(\frac{-2}{5}+\frac{7}{21}=\frac{-42}{105}+\frac{35}{105}=\frac{-7}{105}=\frac{-1}{15}\)
a ) \(\left(-\frac{40}{52}.0,32.\frac{17}{20}\right):\frac{64}{75}\)
= \(\left(-\frac{16}{65}.\frac{17}{20}\right):\frac{64}{75}\)
= \(\left(-\frac{68}{325}\right):\frac{64}{75}\)
= \(\frac{-51}{208}\)
b ) \(-\frac{10}{11}.\frac{8}{9}+\frac{7}{18}.\frac{10}{11}\)
= \(\frac{10}{11}.\left(-\frac{8}{9}+\frac{7}{18}\right)\)
= \(\frac{10}{11}.\left(-\frac{1}{2}\right)\)
= \(\frac{-5}{11}\)
c ) \(\frac{45^{10}.5^{20}}{75^{15}}\)
= \(\frac{5^{10}.3^{20}.5^{20}}{5^{30}.3^{15}}\)
= \(\frac{5^{30}.3^{20}}{5^{30}.3^{15}}\)
= 3 5
= 243
d ) ( - 0,125 ) 3 . 80 4
= -80000
e, \(\frac{3}{14}:\frac{1}{28}-\frac{13}{21}:\frac{1}{28}+\frac{28}{42}:\frac{1}{28}-8\)
\(=\left(\frac{3}{14}-\frac{13}{21}+\frac{2}{3}\right):\frac{1}{28}-8\)
\(=\frac{11}{42}:\frac{1}{28}-8\)
\(=\frac{22}{3}-8\)
\(=-\frac{2}{3}\)
e, \(\frac{3}{14}:\frac{1}{28}-\frac{13}{21}:\frac{1}{28}+\frac{28}{42}:\frac{1}{28}-8\)
\(=\left(\frac{3}{14}-\frac{13}{21}+\frac{2}{3}\right):\frac{1}{28}-8\)
\(=\frac{11}{42}:\frac{1}{28}-8\)
\(=\frac{22}{3}-8\)
\(=-\frac{2}{3}\)
B. 1/3 - 1/3 - 3/5 +3/5 + 5/7 - 5/7 + 9/11 - 9/11 -11/13 + 11/ 13 + 7/9 + 13/15
= 0 -0-0-0-0+7/9 +13/15
= 74/45
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{2}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)
\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(A=1-\frac{1}{10}\)
\(A=\frac{9}{10}\)(đáp án của p sai nha)
= 1 / 1*2 + 1 / 2*3 + 1/ 3*4 + 1 / 4 * 5 ... + 1/ 9*10 = 1-1/2 + 1/2 -1/3 +... + 1/9 - 1/10 = 1 - 1/10 = 9 /10
đáp án của bạn bị sai rùi
#)Well ! Bài này cg dạng tầm cỡ vừa :v
Làm cho ai v ? mau vô nhận bài đê !
ờ tụi làm cho bạn trên lớp í mà
Mà tui ngu quá nhóm lun từ số 1 nhanh hơn ko
a) \(\frac{7}{15}+\frac{9}{10}+\frac{8}{15}-\frac{-1}{10}-\frac{20}{10}+\frac{1}{157}\)
\(=\frac{7}{15}+\frac{9}{10}+\frac{8}{15}+\frac{1}{10}-\frac{20}{10}+\frac{1}{157}\)
\(=\left(\frac{7}{15}+\frac{8}{15}\right)+\left(\frac{9}{10}+\frac{1}{10}\right)-2+\frac{1}{157}\)
\(=1+1-2+\frac{1}{157}\)
\(=2-2+\frac{1}{157}\)
\(=0+\frac{1}{157}=\frac{1}{157}\)
b) \(\frac{1}{13}+\frac{16}{7}+\frac{3}{105}-\frac{9}{7}-\frac{-12}{13}\)
\(=\frac{1}{13}+\frac{16}{7}+\frac{1}{35}-\frac{9}{7}+\frac{12}{13}\)
\(=\left(\frac{1}{13}+\frac{12}{13}\right)+\left(\frac{16}{7}-\frac{9}{7}\right)+\frac{1}{35}\)
\(=1+1+\frac{1}{35}\)
\(=2+\frac{1}{35}\)
\(=\frac{70}{35}+\frac{1}{35}=\frac{71}{35}\)
Bài 1:
a) \(x-\frac{20}{11.13}-\frac{20}{13.15}-...-\frac{20}{53.55}=\frac{3}{11}\)
\(x-\left(\frac{20}{11.13}+\frac{20}{13.15}+...+\frac{20}{53.55}\right)=\frac{3}{11}\)
\(x-\frac{20}{2}.\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{53}-\frac{1}{55}\right)=\frac{3}{11}\)
\(x-10.\left(\frac{1}{11}-\frac{1}{55}\right)=\frac{3}{11}\)
\(x-10\cdot\frac{4}{55}=\frac{3}{11}\)
\(x-\frac{8}{11}=\frac{3}{11}\)
\(x=1\)
b) \(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+...+\frac{2}{x.\left(x+1\right)}=\frac{2}{9}\)
\(\frac{2}{42}+\frac{2}{56}+\frac{2}{72}+...+\frac{2}{x.\left(x+1\right)}=\frac{2}{9}\)
\(\frac{2}{6.7}+\frac{2}{7.8}+\frac{2}{8.9}+...+\frac{2}{x.\left(x+1\right)}=\frac{2}{9}\)
\(2.\left(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2}{9}\)
\(2.\left(\frac{1}{6}-\frac{1}{x+1}\right)=\frac{2}{9}\)
\(\frac{1}{6}-\frac{1}{x+1}=\frac{1}{9}\)
\(\frac{1}{x+1}=\frac{1}{18}\)
=> x + 1 =18
x = 17
bài 2 ko bk lm, xl nha
\(\frac{1}{15}\)chứ ko phải \(\frac{1}{5}\)nha các bạn
\(\frac{1}{5}+\frac{9}{10}+\frac{14}{15}-\frac{1}{9}-\frac{20}{10}+\frac{1}{157}\)
\(=\frac{3}{15}+\frac{9}{10}+\frac{14}{15}-\frac{1}{9}-\frac{20}{10}+\frac{1}{157}\)
\(=\left(\frac{3}{15}+\frac{14}{15}\right)+\left(\frac{9}{10}-\frac{20}{10}\right)-\frac{1}{9}+\frac{1}{157}\)
\(=\frac{17}{15}+\frac{-11}{10}-\frac{1}{9}+\frac{1}{157}\)
\(=\left(\frac{51}{45}-\frac{5}{45}\right)+\frac{-11}{10}+\frac{1}{157}\)
\(=\frac{46}{45}+\frac{-11}{10}+\frac{1}{157}\)
\(=\left(\frac{92}{90}+\frac{-99}{90}\right)+\frac{1}{157}\)
\(=\frac{-1099}{14130}+\frac{90}{14130}\)
\(=\frac{-1099}{14130}\)