Giải phương trình : a. |2x-5|=4

* Hướng dẫn giải

$\begin{array}{l}a)\left|2x-5\right|=4\left(1\right)\\ +)x\ge \frac{5}{2}\Rightarrow \left(1\right)\iff 2x-5=4\iff x=\frac{9}{2}(tm)\\ +)x<\frac{5}{2}\Rightarrow \left(1\right)\iff 5-2x=4\iff x=-\frac{1}{2}(tm)\end{array}$

$\begin{array}{l}b)\frac{5x^2-3x}{5}+\frac{3x+1}{4}<\frac{x\left(2x+1\right)}{2}-\frac{3}{2}\\ \iff \frac{4\left(5x^2-3x\right)+5\left(3x+1\right)}{20}<\frac{10x\left(2x+1\right)-3.10}{20}\\ \iff 20x^2-12x+15x+5<20x^2+10x-30\\ \iff 7x>35\iff x>5\end{array}$