So sanh A va B :
A = \(\dfrac{-13}{21}\) Va B = \(\dfrac{9}{-14}\)
b ) A = \(\dfrac{99}{101}\) va B = \(\dfrac{2011}{2013}\)
c ) A= \(\dfrac{15^{11}+4
}{15^{11}+2}\) Va B = \(\dfrac{15^{21}+4}{15^{21}+2}\)
giúp mình với :(
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SGK Kết nối tri thức với cuộc sống - Trang 75
24 tháng 8 2023 lúc 0:29
Số?
a) \(\dfrac{7}{15}+\dfrac{?}{15}=\dfrac{10}{15}\) b) \(\dfrac{9}{8}+\dfrac{2}{?}=\dfrac{11}{8}\) c) \(\dfrac{6}{21}+\dfrac{9}{21}=\dfrac{15}{?}\)
a) \(\dfrac{7}{15}+\dfrac{3}{15}=\dfrac{10}{15}\)
b) \(\dfrac{9}{8}+\dfrac{2}{8}=\dfrac{11}{8}\)
c) \(\dfrac{6}{21}+\dfrac{9}{21}=\dfrac{15}{21}\)
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so sanh
M=\(\left(\dfrac{1}{2^2}-1\right).\left(\dfrac{1}{3^2}-1\right).\left(\dfrac{1}{4^2}-1\right)...\left(\dfrac{1}{100^2}-1\right)\)va \(\dfrac{1}{2}\)
B=\(\dfrac{1}{20}+\dfrac{1}{21}+...+\dfrac{1}{200}va\dfrac{9}{10}\)
C=\(\dfrac{10}{17}+\dfrac{8}{15}+\dfrac{11}{16}va2\)
1 )Ta có
\(M=\left(\dfrac{1}{2^2}-1\right)\cdot\left(\dfrac{1}{3^2}-1\right)\cdot\left(\dfrac{1}{4^2}-1\right)...\left(\dfrac{1}{100^2}-1\right)\)
\(=\left(\dfrac{1}{2}-1\right)\left(\dfrac{1}{2}+1\right)\left(\dfrac{1}{3}-1\right)\left(\dfrac{1}{3}+1\right).....\left(\dfrac{1}{100}-1\right)\left(\dfrac{1}{100}+1\right)\)
\(=\dfrac{-1}{2}\cdot\dfrac{3}{2}\cdot\dfrac{-2}{3}\cdot\dfrac{4}{3}\cdot\dfrac{-3}{4}\cdot\dfrac{5}{4}\cdot\cdot\cdot\cdot\dfrac{-99}{100}\cdot\dfrac{101}{100}\)
\(=\dfrac{-1\cdot\left(-2\right)\cdot\left(-3\right)\cdot3\cdot\left(-4\right)\cdot4\cdot\left(-5\right)\cdot5....\cdot\left(-100\right)\cdot100\cdot101}{2^2\cdot3^2\cdot4^2....\cdot100^2}\)
\(=-\dfrac{101}{200}< \dfrac{1}{2}\)
2 ) Số phân số của biểu thức B là 180 phân số
Ta có
\(\dfrac{1}{20}>\dfrac{1}{200};\dfrac{1}{21}>\dfrac{1}{200};\dfrac{1}{22}>\dfrac{1}{200};....;\dfrac{1}{199}>\dfrac{1}{200}\)
\(\Rightarrow B=\dfrac{1}{20}+\dfrac{1}{21}+...+\dfrac{1}{200}>\dfrac{1}{200}\cdot180=\dfrac{9}{10}\)
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so sanh = cach hop li
a, \(\dfrac{7}{15}va\dfrac{20}{39}\)
b,\(\dfrac{14}{41}va\dfrac{17}{53}\)
c, \(\dfrac{4^{100^{ }}+2}{4^{98}-1}va\dfrac{4^{98^{ }}+2}{4^{96}-1}\)
Tính nhanh :
\(A=\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41};B=\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{-2}{11}+\dfrac{4}{-9}+\dfrac{7}{15}\)
So sanh:
a) \(\dfrac{-13}{39}\) va \(-\dfrac{21}{63}\)
b) \(\dfrac{1}{234567}\) va \(-\dfrac{2}{14}\)
c)\(\dfrac{-39}{65}\) va \(-\dfrac{21}{35}\)
d) \(\dfrac{1}{2012}\) va \(-\dfrac{1}{14}\)
a, Ta có:
\(\dfrac{-13}{39}=\dfrac{-1}{3}\) và \(-\dfrac{21}{63}=\dfrac{-1}{3}\)
Vì \(\dfrac{-1}{3}=\dfrac{-1}{3}\) nên \(\dfrac{-13}{39}=-\dfrac{21}{63}\)
b, Ta có:
\(\dfrac{1}{234567}>0\) (số hữu tỉ dương) và \(-\dfrac{2}{14}< 0\) (số hữu tỉ âm)
=> \(\dfrac{1}{234567}>-\dfrac{2}{14}\)
c\(\dfrac{1}{2012}>-\dfrac{1}{14}\), Ta có:
\(\dfrac{-39}{65}=\dfrac{-3}{5}\) và \(-\dfrac{21}{35}=\dfrac{-3}{5}\)
mà \(\dfrac{-3}{5}=\dfrac{-3}{5}\) nên \(\dfrac{-39}{65}=-\dfrac{21}{35}\)
d,Ta có:
\(\dfrac{1}{2012}>0\) (số hữu tỉ dương) và \(-\dfrac{1}{14}< 0\) (số hữu tỉ âm)
Vậy suy ra: \(\dfrac{1}{2012}>-\dfrac{1}{14}\)
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tính
a)\(\dfrac{-10}{11}.\dfrac{8}{9}+\dfrac{7}{18}.\dfrac{10}{11}\)
b)\(\dfrac{3}{14}:\dfrac{1}{28}-\dfrac{13}{21}:\dfrac{1}{28}+\dfrac{29}{42}:\dfrac{1}{28}-8\)
c)\(-1\dfrac{5}{7}.15+\dfrac{2}{7}\left(-15\right)+\left(-105\right).\left(\dfrac{2}{3}-\dfrac{4}{5}+\dfrac{1}{7}\right)\)
ăn lồn cái địt mẹ mày lửa trùa ĐẦU LỒN nhá
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Xem thêm câu trả lời
a) \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)
b) \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)
c) \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)
a) Ta có: \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)
nên -11<x<-8
hay \(x\in\left\{-10;-9\right\}\)
b) Ta có: \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)
\(\Leftrightarrow\dfrac{9}{21}< \dfrac{x}{21}< \dfrac{14}{21}\)
Suy ra: 9<x<14
hay \(x\in\left\{10;11;12;13\right\}\)
c) Ta có: \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)
nên \(\dfrac{-536}{168}< \dfrac{x}{168}< \dfrac{-63}{168}\)
Suy ra: -536<x<-63
hay \(x\in\left\{-535;-534;...;-64\right\}\)
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Hoàn thành phép tính :
a) \(\dfrac{7}{9}-\dfrac{....}{3}=\dfrac{1}{9}\)
b) \(\dfrac{1}{......}-\dfrac{-2}{15}=\dfrac{7}{15}\)
c) \(\dfrac{-11}{14}-\dfrac{-4}{.....}=\dfrac{-3}{14}\)
d) \(\dfrac{....}{21}-\dfrac{2}{3}=\dfrac{5}{21}\)
Thay dấu ba chấm bởi x rồi tìm x.
Chẳng hạn:
\(a) \) \(\dfrac{7}{9}-\dfrac{x}{3}=\dfrac{1}{9}\)
\(\Rightarrow\dfrac{x}{3}=\dfrac{7}{9}-\dfrac{1}{9}\)
\(\Rightarrow\dfrac{x}{3}=\dfrac{6}{9}=\dfrac{2}{3}\)
Vậy x = 2
Đáp số:
a) x = 2
b) x = 3
c) x = 7
d) x =19.
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