Đáp án:
a) 1
Giải thích các bước giải:
\(\begin{array}{l}
a)Do:x - y = 5\\
\to x = y + 5\\
Thay:x = y + 5\\
\to \dfrac{{3\left( {y + 5} \right) - y}}{{2\left( {y + 5} \right) + 5}} + \dfrac{{3y - y - 5}}{{2y - 5}}\\
= \dfrac{{2y + 15}}{{2y + 15}} + \dfrac{{2y - 5}}{{2y - 5}} = 1 + 1 = 2\\
b)Do:\dfrac{a}{b} = \dfrac{3}{4}\\
\to a = \dfrac{3}{4}b\\
Thay:a = \dfrac{3}{4}b\\
\to \dfrac{{2.\dfrac{3}{4}b - 5b}}{{\dfrac{3}{4}b - 3b}} = \dfrac{{\dfrac{3}{2}b - 5b}}{{ - \dfrac{9}{4}b}}\\
= \dfrac{{ - 7}}{2}b: - \dfrac{9}{4}b = \dfrac{{14}}{9}
\end{array}\)
