cho x/2=y/5=z/7 tính A=x-y+z/x+2y-z Question cho x/2=y/5=z/7 tính A=x-y+z/x+2y-z in progress 0 Môn Toán Khang Minh 4 years 2020-10-29T02:25:44+00:00 2020-10-29T02:25:44+00:00 1 Answers 104 views 0
Answers ( )
Đáp án:
\[A = \dfrac{4}{5}\]
Giải thích các bước giải:
Đặt \(\dfrac{x}{2} = \dfrac{y}{5} = \dfrac{z}{7} = a\), ta có:
\(\begin{array}{l}
\dfrac{x}{2} = \dfrac{y}{5} = \dfrac{z}{7} = a \Rightarrow \left\{ \begin{array}{l}
x = 2a\\
y = 5a\\
z = 7a
\end{array} \right.\\
A = \dfrac{{x – y + z}}{{x + 2y – z}} = \dfrac{{2a – 5a + 7a}}{{2a + 2.5a – 7a}} = \dfrac{{4a}}{{5a}} = \dfrac{4}{5}
\end{array}\)
Vậy \(A = \dfrac{4}{5}\)