1.

$-7(5-x)-2(x-10)=15$

$-35+7x-2x+20=15$

$5x-15=15$

$5x=30$

$x=30:5=6$

2.

$3(x-4)-(8-x)=12$

$3x-12-8+x=12$

$4x-20=12$

$4x=12+20=32$

$x=32:4=8$

\(\left(x-2\right)\left(xy-1\right)=5=1\cdot5=5\cdot1=-1\cdot-5=-5\cdot-1\)

Ta có bảng sau: 

Vậy: ...

\(\left(x+5\right)\left(7+x\right)=0\)

TH1: \(x+5=0\)

\(\Rightarrow x=-5\)

TH2: \(7+x=0\)

\(\Rightarrow x=-7\)

Vậy: \(x\in\left\{-5;-7\right\}\)

\(\left(x+5\right).\left(7+x\right)=0\)

\(\left(1\right):x+5=0\)

        \(x=0-5\Rightarrow x=-5.\)

\(\left(2\right):7+x=0\)

        \(x=0-7\Rightarrow x=-7\)

Từ \(\left(1\right)\) và \(\left(2\right)\):

\(\Rightarrow\left\{{}\begin{matrix}x=-5\\x=-7\end{matrix}\right.\)

(-23).35 + 35.(-37) + 65.(-60)

= 35.(-23-37) + 65.(-60) 

= 35.(-60) + 65.(-60) 

= (-60).(35 + 65) 

= (-60).100

= -6000

110

77 33 + 110

Ta có: \(\left(3x-6\right)\left(5-x\right)\ge0\Leftrightarrow\left[{}\begin{matrix}\left(3x-6\right)\left(5-x\right)>0\\\left(3x-6\right)\left(5-x\right)=0\end{matrix}\right.\)

+, Trường hợp 1: \(\left(3x-6\right)\left(5-x\right)>0\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}3x-6>0\\5-x>0\end{matrix}\right.\\\left\{{}\begin{matrix}3x-6< 0\\5-x< 0\end{matrix}\right.\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}3x>6\\5>x\end{matrix}\right.\\\left\{{}\begin{matrix}3x< 6\\5< x\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>2\\x< 5\end{matrix}\right.\\\left\{{}\begin{matrix}x< 2\\x>5\end{matrix}\right.\left(\text{vô lí}\right)\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x>2\\x< 5\end{matrix}\right.\Leftrightarrow2< x< 5\)

+, Trường hợp 2: \(\left(3x-6\right)\left(5-x\right)=0\Leftrightarrow\left[{}\begin{matrix}3x-6=0\\5-x=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}3x=6\\x=5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=5\end{matrix}\right.\)

Vậy biểu thức \(\left(3x-6\right)\left(5-x\right)\) lớn hơn 0 khi \(2< x< 5\) và bằng 0 khi \(x\in\left\{2;5\right\}\).

-(2012-199+20)-(-199+20)

=-2012+199-20+199-20

=-2012+(200-1)-20+(200-1)-20

=-2012+200+200-1-1-20-20

=-2012+(200+200)-(20+20+1+1)

=-2012+400-42

=-1612-42=-1654

1) Do x ∈ Z và 0 < x < 3

⇒ x ∈ {1; 2}

2) Do x ∈ Z và 0 < x ≤ 3

⇒ x ∈ {1; 2; 3}

3) Do x ∈ Z và -1 < x ≤ 4

⇒ x ∈ {0; 1; 2; 3; 4}

=73 nha bạn

73 cậu nha