Bạn cần bài nào :v?

Em đăng tách bài nha 1-2 bài/1 lần hỏi

bài 1: 

\(\left\{{}\begin{matrix}x+y=57\\4x-2y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x+4y=228\\4x-2y=6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}6y=234\\x+y=57\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=39\\x=18\end{matrix}\right.\)

-9/6

=\(-\dfrac{3}{2}\)

\(\dfrac{1}{6}+\dfrac{-5}{3}=\dfrac{2}{12}+\dfrac{-20}{12}=\dfrac{-18}{12}=\dfrac{\left(-18\right):6}{12:6}=\dfrac{-3}{2}\)

A = 3\(x^2\) + 9\(x\) - 7

A = 3.(\(x^2\) + 3\(x\) + \(\dfrac{9}{4}\)) - 7

A = 3.(\(x\) + \(\dfrac{3}{2}\))² - \(\dfrac{55}{4}\)

Vì (\(x\) + \(\dfrac{3}{2}\))² ≥ 0; ⇒ 3.(\(x\) + \(\dfrac{3}{2}\))² - \(\dfrac{55}{4}\) ≥ - \(\dfrac{55}{4}\)

A(min) = - \(\dfrac{55}{4}\) ⇔ \(x\) + \(\dfrac{3}{2}\) = 0 ⇔ \(x\) = - \(\dfrac{3}{2}\) 

Bài 2 : a, x = -36/9 = -4

b, đề sai 

c, <=> -2 =< x =< -3 => x = -1 

Bài 1: 

a: 2/8=9/36; 2/9=8/36; 8/2=36/9; 9/2=36/8

b: -2/4=9/-18; -2/9=4/-18; 4/-2=-18/9; 9/-2=-18/4

Bài 2: 

a: =>x/3=-4/3

hay x=-4

Câu b đề sai rồi bạn