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3x . 2 + 15 = 33
3x . 2 = 33 - 15 = 18
3x = 18 : 2 = 9 = 32
=> x = 2
a. Chu vi là \(\left(12+5\right).2=34\left(m\right)\)
Diện tích là \(12.5=60\left(m^2\right)=600000\left(cm^2\right)\)
b. Cần lát \(600000:\left(40.40\right)=375\) viên gạch
\(\Leftrightarrow164-4\left(x-5\right)=80\\ \Leftrightarrow4\left(x-5\right)=84\\ \Leftrightarrow x-5=21\Leftrightarrow x=26\)
help me, pls. Sắp đến giờ nộp bài rồi, các bn giúp mình với
c: Trường hợp 1: n=2k
\(\Leftrightarrow n\left(n+2017\right)=2k\left(2k+2017\right)⋮2\)
Trường hợp 2: n=2k+1
\(\Leftrightarrow n\left(n+2017\right)=\left(2k+1\right)\left(2k+2018\right)⋮2\)
\(B=2+2^2+2^3+2^4+...+2^{99}+2^{100}=2\left(1+2^2+2^3+2^4\right)+...+2^{96}\left(1+2^2+2^3+2^4\right)=2.31+2^6.31+...+2^{96}.31=31\left(2+2^6+...+2^{96}\right)⋮31\)
\(A=7\left(1+7+7^2\right)+...+7^{118}\left(1+7+7^2\right)\)
\(=57\left(1+...+7^{118}\right)⋮57\)
1: \(\dfrac{21}{-20}-\dfrac{11}{5}-\dfrac{-5}{4}\)
\(=-\dfrac{21}{20}-\dfrac{11}{5}+\dfrac{5}{4}\)
\(=-\dfrac{21}{20}-\dfrac{44}{20}+\dfrac{25}{20}=\dfrac{-40}{20}=-2\)
2: \(\dfrac{-1}{6}-\dfrac{4}{-3}-\dfrac{11}{18}\)
\(=\dfrac{-1}{6}+\dfrac{4}{3}-\dfrac{11}{18}\)
\(=-\dfrac{3}{18}+\dfrac{24}{18}-\dfrac{1}{18}=\dfrac{10}{18}=\dfrac{5}{9}\)
3: \(\dfrac{7}{17}-\dfrac{5}{-2}+\dfrac{13}{34}\)
\(=\dfrac{7}{17}+\dfrac{5}{2}+\dfrac{13}{34}\)
\(=\dfrac{14}{34}+\dfrac{85}{34}+\dfrac{13}{34}=\dfrac{112}{34}=\dfrac{56}{17}\)
4: \(\left(\dfrac{3}{29}-\dfrac{1}{5}\right)\cdot\dfrac{29}{3}\)
\(=\left(\dfrac{15}{145}-\dfrac{29}{145}\right)\cdot\dfrac{29}{3}\)
\(=\dfrac{-14}{145}\cdot\dfrac{29}{3}=-\dfrac{14}{3}\cdot\dfrac{29}{145}=\dfrac{-14}{15}\)
5: \(\dfrac{3}{4}:\dfrac{7}{8}-3\dfrac{1}{4}+1\)
\(=\dfrac{3}{4}\cdot\dfrac{8}{7}-\dfrac{13}{4}+1\)
\(=\dfrac{6}{7}-\dfrac{9}{4}\)
\(=\dfrac{24}{28}-\dfrac{54}{28}=\dfrac{-30}{28}=-\dfrac{15}{14}\)
6: \(\left(0,75+\dfrac{-1}{3}-\dfrac{5}{8}\right):\dfrac{-5}{6}\)
\(=\left(\dfrac{3}{4}-\dfrac{1}{3}-\dfrac{5}{8}\right):\dfrac{-5}{6}\)
\(=\left(\dfrac{18}{24}-\dfrac{8}{24}-\dfrac{15}{24}\right):\dfrac{-5}{6}\)
\(=\dfrac{-5}{24}\cdot\dfrac{6}{-5}=\dfrac{6}{24}=\dfrac{1}{4}\)
7: \(3\dfrac{1}{7}-\dfrac{1}{4}\cdot\dfrac{2}{9}+25\%\)
\(=\dfrac{22}{7}-\dfrac{1}{18}+\dfrac{1}{4}\)
\(=\dfrac{841}{252}\)
8: \(4\dfrac{1}{5}-\dfrac{1}{5}\cdot\dfrac{10}{11}+15\%\)
\(=\dfrac{21}{5}-\dfrac{2}{11}+\dfrac{3}{20}\)
\(=\dfrac{924}{220}-\dfrac{40}{220}+\dfrac{66}{220}=\dfrac{950}{220}=\dfrac{95}{22}\)
9: \(1\dfrac{1}{2}-1\dfrac{2}{5}\cdot1,5-2,2:\dfrac{11}{4}\)
\(=\dfrac{3}{2}-\dfrac{7}{5}\cdot\dfrac{3}{2}-2,2\cdot\dfrac{4}{11}\)
\(=\dfrac{3}{2}\left(1-\dfrac{7}{5}\right)-\dfrac{8.8}{11}\)
\(=\dfrac{3}{2}\cdot\dfrac{-2}{5}-\dfrac{4}{5}=-\dfrac{3}{5}-\dfrac{4}{5}=-\dfrac{7}{5}\)
10: \(\dfrac{3}{17}\cdot\dfrac{13}{15}+\dfrac{3}{17}\cdot\dfrac{2}{15}\)
\(=\dfrac{3}{17}\left(\dfrac{13}{15}+\dfrac{2}{15}\right)=\dfrac{3}{17}\cdot\dfrac{15}{15}=\dfrac{3}{17}\)
11: \(\dfrac{7}{19}\cdot\dfrac{8}{11}+\dfrac{7}{19}\cdot\dfrac{3}{11}+\dfrac{-14}{19}\)
\(=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)-\dfrac{14}{19}=\dfrac{7}{19}-\dfrac{14}{19}=-\dfrac{7}{19}\)
12: \(\dfrac{-4}{5}\cdot\dfrac{7}{11}+\dfrac{-4}{5}\cdot\dfrac{4}{11}+1\dfrac{2}{11}\)
\(=\dfrac{-4}{5}\left(\dfrac{7}{11}+\dfrac{4}{11}\right)+1+\dfrac{2}{11}=-\dfrac{4}{5}+1+\dfrac{2}{11}\)
\(=\dfrac{1}{5}+\dfrac{2}{11}=\dfrac{11}{55}+\dfrac{10}{55}=\dfrac{21}{55}\)