Giải bài 25 luyện tập trang 16 - SGK Toán lớp 7 Tập 1

$+) \mathrm{Với} <span\; class="math-tex">\backslash (\; x\; +\; \backslash dfrac\{3\}\{4\}\; =\; \backslash dfrac\{1\}\{3\}\; \backslash Leftrightarrow\; x\; =\; \backslash dfrac\{1\}\{3\}\; -\; \backslash dfrac\{3\}\{4\}\; =\; \backslash dfrac\{4\}\{12\}\; -\; \backslash dfrac\{9\}\{12\}\; =\; \backslash dfrac\{-5\}\{12\}\; \backslash )</span>$

$+) \mathrm{Với} <span\; class="math-tex">\backslash (\; x\; +\; \backslash dfrac\{3\}\{4\}\; =\; -\backslash dfrac\{1\}\{3\}\; \backslash Leftrightarrow\; x\; =\; -\backslash dfrac\{1\}\{3\}\; -\; \backslash dfrac\{3\}\{4\}\; =\; -\backslash dfrac\{4\}\{12\}\; -\; \backslash dfrac\{9\}\{12\}\; =\; \backslash dfrac\{-13\}\{12\}\; \backslash )</span>$

$\mathrm{Vậy} <span\; class="math-tex">\backslash (x\; =\; -\backslash dfrac\{5\}\{12\}\backslash )</span> \mathrm{hoặc} <span\; class="math-tex">\backslash (x\; =\; -\backslash dfrac\{13\}\{12\}\backslash )</span>$

Lưu ý:  \(|x| = \left\{\begin{array}{l} x \,\,\text{nếu} \,\,x \geq 0 \\ -x \,\,\text{nếu} \,\,x < 0\end{array} \right.\)