1
$\frac{۱}{۲}({{a}^{۲}}-{{b}^{۲}})$
✓
✗
2
$\frac{۱}{۲}({{a}^{۲}}+{{b}^{۲}})$
✓
✗
3
$\frac{۱}{۲}{{(a+b)}^{۲}}$
✓
✗
4
$\frac{۱}{۲}{{(a-b)}^{۲}}$
✓
✗
خطا
در $HB=\frac{\sqrt{2}}{2}a\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,:\,\overset{\vartriangle }{\mathop{AHB}}\,$ در $BG=\frac{\sqrt{2}}{2}b\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,:\,\overset{\vartriangle }{\mathop{BGC}}\,$ $HG=HB-BG=\frac{\sqrt{2}}{2}(a-b)\Rightarrow {{S}_{EFGH}}={{\left[ \frac{\sqrt{2}}{2}(a-b) \right]}^{2}}=\frac{{{(a-b)}^{2}}}{2}$