七个面积公式
<span class="equation-text" contenteditable="false" data-index="0" data-equation="基本面积公式 ：S△={1 \over 2}ah ；其中a为底边长，h为高"><span></span><span></span></span>
三角函数面积公式：<span class="equation-text" contenteditable="false" data-index="0" data-equation="S△={1\over 2} absinC；其中sinC为a,b边的夹角正弦函数"><span></span><span></span></span>
<span class="equation-text" contenteditable="false" data-index="0" data-equation="海伦公式：S△=\sqrt{p(p-a)(p-b)(p-c)}；其中p={a+b+c \over 2}"><span></span><span></span></span>
S△=<span class="equation-text" contenteditable="false" data-index="0" data-equation="{1 \over 2}r(a+b+c)；其中r为内接圆的半径"><span></span><span></span></span>
<span class="equation-text" contenteditable="false" data-index="0" data-equation="S△={abc \over 4R}；其中R为外接圆的半径"><span></span><span></span></span>
S△=Rr(SinA+SinB+SinC)；其中R为外接圆的半径，r为内接圆的半径
S△=2<span class="equation-text" contenteditable="false" data-index="0" data-equation="R^2SinASinBSinC；其中R为外接圆的半径"><span></span><span></span></span>
