Giải các bất phương trình:

a) $\frac{2-x}{4}<5$                                                b) $3\le \frac{2x+3}{5}$

c) $\frac{4x-5}{3}>\frac{7-x}{5}$                                       d) $\frac{2x+3}{-4}\ge \frac{4-x}{-3}$

Hướng dẫn:

a) $\iff 2-x<5.4\iff -x<20-2\iff x>-18$

b) $\iff 3.5\le 2x+3\iff 15-3\le 2x\iff 6\le x\iff x\ge 6$

c) $\iff 5(4x-5)>3(7-x)\iff 20x-25>21-3x$

   $\iff 20x+3x>21+25\iff 23x>46\iff x>2$

d) $-3(2x+3)\le -4(4-x)\iff -6x-9\le 16+4x$

   $\iff -6x-4x\le -16+9\iff -10x\le -7\iff x\ge 0,7$