0,25 của -30 là -30 x 0,25 = -7,5

-2975 nhé

2,000000246

khoảng cách giữa hai thành phố  trong thực tế là:

11000000:84=130952(km)

đáp số;130925 km

\(A=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+...+\frac{2}{16.19}\)

\(A=\frac{2}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{16.19}\right)\)

\(A=\frac{2}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{16}-\frac{1}{19}\right)\)

\(A=\frac{2}{3}.\left(1-\frac{1}{19}\right)\)

\(A=\frac{2}{3}.\frac{18}{19}=\frac{12}{19}\)

\(A=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}+\frac{2}{16.19}\)

\(=\frac{2}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{16}-\frac{1}{19}\right)\)

\(=\frac{2}{3}\left(1-\frac{1}{19}\right)=\frac{2}{3}.\frac{18}{19}=\frac{36}{57}=\frac{12}{19}\)

\(A=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}+\frac{2}{16.19}\)

\(\frac{3}{2}A=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}+\frac{3}{16.19}\)

\(\frac{3}{2}A=\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+\frac{13-10}{10.13}+\frac{16-13}{13.16}+\frac{19-16}{16.19}\)

\(\frac{3}{2}A=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}+\frac{1}{16}-\frac{1}{19}\)

\(\frac{3}{2}A=1-\frac{1}{19}\)

\(A=\frac{2}{3}.\frac{18}{19}=\frac{12}{19}\)

     \(\frac{x-2}{3}=\frac{x+4}{5}\)

\(\Rightarrow\)\(5\left(x-2\right)=3\left(x+4\right)\)

\(\Rightarrow\)\(5x-10=3x+12\)

\(\Rightarrow\)\(5x-3x=10+12\)

\(\Rightarrow\)\(2x=22\)

\(\Rightarrow\)\(x=11\)