Đáp án:
1.a,\(\frac{{ - 7}}{{10}}\)
b,0
c,-14
2.\(x = 2\),\(y = \frac{{ - 1}}{{15}}\)
Giải thích các bước giải:
\(\begin{array}{l}
1.\\
a,\frac{{ - 2}}{5} + \frac{3}{{10}} + \frac{{ - 3}}{5}\\
= (\frac{{ - 2}}{5} + \frac{{ - 3}}{5}) + \frac{3}{{10}}\\
= - 1 + \frac{3}{{10}}\\
= \frac{{ - 7}}{{10}}\\
b,9.{(\frac{{ - 1}}{3})^3} + \frac{1}{6}.\sqrt 4 \\
= 9.\frac{{ - 1}}{{27}} + \frac{1}{6}.2\\
= \frac{{ - 1}}{3} + \frac{1}{3}\\
= 0\\
c,15\frac{1}{4}:\frac{5}{7} - 25\frac{1}{4}:\frac{5}{7}\\
= (15\frac{1}{4} - 25\frac{1}{4}):\frac{5}{7}\\
= - 10.\frac{7}{5}\\
= - 14\\
2.\frac{{1 + 3y}}{{12}} = \frac{{1 + 5y}}{{5x}} = \frac{{1 + 7y}}{{4x}}\\
\Rightarrow 4(1 + 5y) = 5(1 + 7y)\\
\Leftrightarrow y = \frac{{ - 1}}{{15}}\\
\Rightarrow x = 2
\end{array}\)
