\(x-\frac{1}{15}=\frac{1}{10}\)

\(x=\frac{1}{10}+\frac{1}{15}\)

\(x=\frac{5}{3}\)

Vậy \(x=\frac{5}{3}\)

\(-\frac{2}{15}-x=-\frac{3}{10}\)

\(x=-\frac{2}{15}+\frac{3}{10}\)

\(x=\frac{1}{15}\)

Vậy \(x=\frac{1}{15}\)

\(x-\frac{1}{15}=\frac{1}{10}\)

\(\Rightarrow x=\frac{1}{10}+\frac{1}{15}\)

\(\Rightarrow x=\frac{1}{6}\)

\(\frac{-2}{15}-x=\frac{-3}{10}\)

\(\Rightarrow x=\frac{-2}{15}-\frac{-3}{10}\)

\(\Rightarrow x=\frac{1}{6}\)

= 1/3 - 1/3 + 5/7 - 5/7 - 7/9 + 7/9 +9/11 - 9/11 -11/13 + 11/13 +13/15

= 0 + 0 - 0 + 0 -0 + 13/15

= 0 + 13/15

= 13/15

\(\frac{1}{3}-\frac{3}{5}+\frac{5}{7}-\frac{7}{9}+\frac{9}{11}-\frac{11}{13}+\frac{13}{15}+\frac{11}{13}-\frac{9}{11}+\frac{7}{9}-\frac{5}{7}+\frac{3}{5}-\frac{1}{3}\)

\(=\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{3}{5}-\frac{3}{5}\right)+\left(\frac{5}{7}-\frac{5}{7}\right)+\left(\frac{7}{9}-\frac{7}{9}\right)+\left(\frac{9}{11}-\frac{9}{11}\right)+\left(\frac{11}{13}-\frac{11}{13}\right)+\frac{13}{15}\)

\(=0+0+0+0+0+0+\frac{13}{15}\)

\(=\frac{13}{15}\)

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b) Câu hỏi của Trần Ngô Hạ Uyên - Toán lớp 7 - Học toán với OnlineMath

b. Ta có \(x:y:z=2:5:3\)nên nếu gọi x=2a thì y=5a;z=3a

Từ đó \(x+3y-2z=2a+3.5a-2.3a=-22\Leftrightarrow11a=-22\Leftrightarrow a=-2\)

\(\Rightarrow x=2a=-4\); \(y=5a=-10\); \(z=3a=-6\)

Vậy ......

\(\frac{a-1}{2}=\frac{b+3}{4}=\frac{c-5}{6}=\frac{5a-5}{10}=\frac{3b+9}{12}=\frac{4c-20}{24}=.\)

\(=\frac{5a-5-3b-9-4c+20}{10-12-24}=\frac{5a-3b-4c+6}{-26}=\frac{46+6}{-26}=-2\)

\(\Rightarrow\frac{a-1}{2}=-2\Rightarrow a=-3\)

b; c tìm tương tự

Tìm x , biết :

1 , | x + 2 | - | x + 1 | = 0

2 , | x + 1 | + | x + 4 | = 3x

3 , | 2x - 1 | \(\le\)5