Tìm x biết: <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mo" id="MJXp-Span-2" style="margin-left: 0em; margin-right: 0.222em;"></span><span class="MJXp-mo" id="MJXp-Span-3" style="margin-left: 0em; margin-right: 0.222em;"></span><span class="MJXp-mstyle" id="MJXp-Span-4"><span class="MJXp-mstyle" id="MJXp-Span-5"><span class="MJXp-mfrac" id="MJXp-Span-6" style="vertical-align: 0.25em;"><span class="MJXp-box"><span class="MJXp-mn" id="MJXp-Span-7">15</span></span><span class="MJXp-box" style="margin-top: -0.9em;"><span class="MJXp-denom"><span><span class="MJXp-rule" style="height: 1em; border-top: none; border-bottom: 1px solid; margin: 0.1em 0px;"></span></span><span><span class="MJXp-box"><span class="MJXp-mn" id="MJXp-Span-8">12</span></span></span></span></span></span></span><span class="MJXp-mo" id="MJXp-Span-9" style="margin-left: 0.267em; margin-right: 0.267em;">−</span><span class="MJXp-mstyle" id="MJXp-Span-10"><span class="MJXp-mfrac" id="MJXp-Span-11" style="vertical-align: 0.25em;"><span class="MJXp-box"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-12">x</span></span><span class="MJXp-box" style="margin-top: -0.9em;"><span class="MJXp-denom"><span><span class="MJXp-rule" style="height: 1em; border-top: none; border-bottom: 1px solid; margin: 0.1em 0px;"></span></span><span><span class="MJXp-box"><span class="MJXp-mn" id="MJXp-Span-13">4</span></span></span></span></span></span></span><span class="MJXp-mo" id="MJXp-Span-14" style="margin-left: 0.333em; margin-right: 0.333em;">=</span><span class="MJXp-mstyle" id="MJXp-Span-15"><span class="MJXp-mfrac" id="MJXp-Span-16" style="vertical-align: 0.25em;"><span class="MJXp-box"><span class="MJXp-mn" id="MJXp-Span-17">13</span></span><span class="MJXp-box" style="margin-top: -0.9em;"><span class="MJXp-denom"><span><span class="MJXp-rule" style="height: 1em; border-top: none; border-bottom: 1px solid; margin: 0.1em 0px;"></span></span><span><span class="MJXp-box"><span class="MJXp-mn" id="MJXp-Span-18">20</span></span></span></span></span></span></span></span></span></span><script type="math/tex" id="MathJax-Element-1">\Large\dfrac{15}{12}-\dfrac{x}{4}=\dfrac{13}{20}</script> Giá