Question

Bài 1 : Giải hệ phương trình

a ) \(\left\{{}\begin{matrix}4x-3y=10\\2x+7y=8\end{matrix}\right.\)

b) \(\left\{{}\begin{matrix}4x-y=9\\-x+5y=8\end{matrix}\right.\)

c) \(\left\{{}\begin{matrix}x+3y=10\\5x-y=4\end{matrix}\right.\)

Answer 1

a lm 1 câu mấy câu sau tương tự nha

Ta có: \(\left\{{}\begin{matrix}4x-3y=10\left(1\right)\\2x+7y=8\left(2\right)\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}4x-3y=10\left(1\right)\\4x+14y=16\left(2\right)\end{matrix}\right.\)

Lấy \(\left(2\right)-\left(1\right)\Rightarrow\left(4x+14y\right)-\left(4x-3y\right)=6\)

\(\Leftrightarrow17y=6\)

\(\Leftrightarrow y=\dfrac{6}{17}\)

Thay vào (1) tìm x