1/5 : (𝑥 - 3) + 1/2 = 1 và 1/8
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\(\dfrac{2}{9}\cdot\dfrac{5}{17}+\dfrac{2}{9}\cdot\dfrac{12}{17}-\dfrac{1}{9}\\ \\ \\ =\dfrac{2}{9}\cdot\left(\dfrac{5}{17}+\dfrac{12}{17}\right)-\dfrac{1}{9}\\ \\ \\ =\dfrac{2}{9}\cdot1-\dfrac{1}{9}\\ \\ \\ =\dfrac{2}{9}-\dfrac{1}{9}=\dfrac{1}{9}\)
a) \(\dfrac{2}{1\times4}+\dfrac{2}{4\times7}+\dfrac{2}{7\times10}+...+\dfrac{2}{97\times100}\)
\(=2.\left(\dfrac{1}{1\times4}+\dfrac{1}{4\times7}+\dfrac{1}{7\times10}+...+\dfrac{1}{97\times100}\right)\)
\(=2.\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)
\(=2.\left(1-\dfrac{1}{100}\right)\)
\(=2.\dfrac{99}{100}\)
\(=\dfrac{99}{50}\)
_____
b) \(\dfrac{3}{1\times5}+\dfrac{3}{5\times9}+\dfrac{3}{9\times13}+...+\dfrac{3}{97\times101}\)
\(=3.\left(\dfrac{1}{1\times5}+\dfrac{1}{5\times9}+\dfrac{1}{9\times13}+...+\dfrac{1}{97\times101}\right)\)
\(=3.\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{13}+...+\dfrac{1}{97}-\dfrac{1}{101}\right)\)
\(=3.\left(1-\dfrac{1}{101}\right)\)
\(=3.\dfrac{100}{101}\)
\(=\dfrac{300}{101}\)
a) \(12\dfrac{1}{3}-\left(3\dfrac{3}{4}+4\dfrac{3}{4}\right)=\dfrac{37}{3}-\left(\dfrac{15}{4}+\dfrac{19}{4}\right)\)
\(=\dfrac{37}{3}-\dfrac{34}{4}=\dfrac{37}{3}-\dfrac{17}{2}=\dfrac{74}{6}-\dfrac{51}{6}=\dfrac{23}{6}\)
b) \(3\dfrac{5}{6}+2\dfrac{1}{6}.6=\dfrac{23}{6}+\dfrac{13}{6}.6=\dfrac{23}{6}+\dfrac{78}{6}=\dfrac{101}{6}\)
c) \(3\dfrac{1}{2}+4\dfrac{5}{7}-5\dfrac{5}{14}=\dfrac{7}{2}+\dfrac{33}{7}-\dfrac{75}{14}=\dfrac{49}{14}+\dfrac{66}{14}-\dfrac{75}{14}=-\dfrac{92}{14}=-\dfrac{46}{7}\)
d) \(4\dfrac{1}{2}+\dfrac{1}{2}:5\dfrac{1}{2}=\dfrac{9}{2}+\dfrac{1}{2}:\dfrac{11}{2}=\dfrac{9}{2}+\dfrac{1}{2}.\dfrac{2}{11}=\dfrac{9}{2}+\dfrac{1}{11}=\dfrac{99}{22}+\dfrac{2}{22}=\dfrac{101}{22}\)
a. \(12\dfrac{1}{3}-\left(3\dfrac{3}{4}+4\dfrac{3}{4}\right)=\dfrac{37}{3}-\left(\dfrac{15}{4}+\dfrac{19}{4}\right)\)
\(=\dfrac{37}{3}-\dfrac{34}{4}=\dfrac{23}{6}\)
\(b.3\dfrac{5}{6}+2\dfrac{1}{6}.6=\dfrac{23}{6}+13=\dfrac{101}{6}\)
\(c.3\dfrac{1}{2}+4\dfrac{5}{7}-5\dfrac{5}{14}=\dfrac{7}{2}+\dfrac{33}{7}-\dfrac{75}{14}=\dfrac{20}{7}\)
d \(4\dfrac{1}{2}+\dfrac{1}{2}:5\dfrac{1}{2}\)
\(=\dfrac{9}{2}+\dfrac{1}{2}:\dfrac{11}{2}\)
\(=\dfrac{9}{2}+\dfrac{1}{11}\)
\(=\dfrac{101}{22}\)
a. \(\dfrac{2021+2020.2022}{2021.2022-1}\)
\(\dfrac{2021.2022-2022+2021}{2021.2022-1}=\dfrac{2021.2022-1}{2021.2022-1}=1\)
\(b.\dfrac{2022+2021.2023}{2022.2023-1}=\dfrac{2021.2023-2023+2022}{2022.2023-1}\)
\(=\dfrac{2021.2023-1}{2022.2023-1}\)
a/
\(10^{33}⋮2;8⋮2\Rightarrow\left(10^{33}+8\right)⋮2\)
\(10^{33}+8=999...99+1+8=999...99+9\) (33 chữ số 9)
\(999...99+9⋮9\Rightarrow\left(10^{33}+8\right)⋮9\)
Mà 2 và 9 là 2 số nguyên tố cùng nhau
\(\Rightarrow\left(10^{33}+8\right)⋮2x9\Rightarrow\left(10^{33}+8\right)⋮18\)
b/
\(10^{10}⋮2;14⋮2\Rightarrow\left(10^{10}+14\right)⋮2\)
\(10^{10}+14=999..99+1+14=999...99+15⋮3\) (10 chữ số 9)
\(\Rightarrow\left(10^{10}+14\right)⋮3\)
2 và 3 là 2 số nguyên tố cùng nhau
\(\Rightarrow\left(10^{10}+14\right)⋮2x3\Rightarrow\left(10^{10}+14\right)⋮6\)
a) (1033 +8) ⋮ 18
=> Ta phải CM được (1033 +8) ⋮ 2; (1033 +8) ⋮ 9
+) 1033 +8 = \(\overline{...0}+8=\overline{........8}\)
Vì (1033 +8) có chữ số tận cùng là chẵn => (1033 +8) ⋮ 2
+) (1033 +8) có tổng các chữ số = 9 => (1033 +8) ⋮ 9
CMR: (1033 +8) ⋮ 18
b) (1010 + 14) ⋮ 6
=> Ta phải Cm được (1010 + 14) ⋮2 ;(1010 + 14) ⋮ 3
+) (1010 + 14) = \(\overline{......00}+14=\overline{..........14}\)
Vì (1010 + 14) có chữ số tận cùng là số chẵn => (1010 + 14) ⋮ 2
+) Vì (1010 + 14) có tổng các chữ số = 6 => (1010 + 14) ⋮ 3
đã CMR: (1010 + 14) ⋮6
a,với y=0 thì x=1,4,7
b,với b=0 thì a=1,9
với b=4 thì a=5
với b=8 thì a=2
GT:a, vì số 48x5y chia hết cho 2 và 5 nên y=0
⇒4+8+x+5+0⋮3
⇒17⋮3
⇒.......
b, phân tích 36 thành 4 và 9 và làm tuoưng tự câu a
\(\dfrac{a}{b}=\dfrac{c}{d}\Rightarrow\dfrac{2a}{2b}=\dfrac{3c}{3d}=\dfrac{2a+3c}{2b+3d}=\dfrac{2a-3c}{2b-3d}\)
\(\Rightarrow\dfrac{2a+3c}{2a-3c}=\dfrac{2b+3d}{2b-3d}\)
\(\Rightarrow dpcm\)
\(\dfrac{1}{5}:\left(x-3\right)+\dfrac{1}{2}=1\dfrac{1}{8}\\ \Rightarrow\dfrac{1}{5}:\left(x-3\right)=\dfrac{9}{8}-\dfrac{1}{2}\\ \Rightarrow\dfrac{1}{5}:\left(x-3\right)=\dfrac{9}{8}-\dfrac{4}{8}\\ \Rightarrow\dfrac{1}{5}:\left(x-3\right)=\dfrac{5}{8}\\ \Rightarrow x-3=\dfrac{1}{5}:\dfrac{5}{8}\\ \Rightarrow x-3=\dfrac{8}{25}\\ \Rightarrow x=\dfrac{8}{25}+3\\ \Rightarrow x=\dfrac{83}{25}\)
\(\dfrac{1}{5}:\left(x-3\right)+\dfrac{1}{2}=1\dfrac{1}{8}\)
\(\dfrac{1}{5}:\left(x-3\right)+\dfrac{1}{2}=\dfrac{9}{8}\)
\(\dfrac{1}{5}:\left(x-3\right)=\dfrac{9}{8}-\dfrac{1}{2}=\dfrac{9}{8}-\dfrac{4}{8}\)
\(\dfrac{1}{5}:\left(x-3\right)=\dfrac{5}{8}\)
\(x-3=\dfrac{1}{5}:\dfrac{5}{8}=\dfrac{1}{5}.\dfrac{8}{5}\)
\(x-3=\dfrac{8}{25}\)
\(x=\dfrac{8}{25}+3=\dfrac{8}{25}+\dfrac{75}{25}\)
\(x=\dfrac{83}{25}\)