Bài tập theo tuần Toán 8 _ Tuần 32_ đề 2

Đáp án B

Đáp án A

Đáp án C

Đáp án C

Đáp án C

Đáp án C

$-a+3>-b+3\Rightarrow -a>-b\iff a<b$

$\begin{array}{l}a)-3x-5>0\iff 3x<-5\iff x<\frac{-5}{3}S=\left\{x/x<-\frac{5}{3}\right\}\\ b)\frac{6-2x}{5}\le \frac{7x}{3}\iff \frac{3\left(6-2x\right)-5.7x}{15}\le 0\iff \frac{18-6x-35x}{15}\le 0\\ \iff 41x\ge 18\iff x\ge \frac{18}{41}S=\left\{x/x\ge \frac{18}{41}\right\}\end{array}$

$a+b>b+3\Rightarrow a>b$

$\begin{array}{l}a)-4x-18\le 0\iff 4x\ge -18\iff x\ge \frac{-9}{2}\\ b)3\left(3x-2\right)<2-7x\iff 9x-6<2-7x\iff x<\frac{1}{2}\end{array}$

$\begin{array}{l}{x}^2-1>0\iff \left(x-1\right)\left(x+1\right)>0\\ \Rightarrow \left[\begin{array}{l}\left\{\begin{array}{l}x-1>0\\ x+1>0\end{array}\right.\\ \left\{\begin{array}{l}x-1<0\\ x+1<0\end{array}\right.\end{array}\right.\iff \left[\begin{array}{l}x>1\\ x<-1\end{array}\right.\end{array}$