Hi
An easy way to calculate the area of the polygon is to close it (adding again the first vertice at the end).
In this case, the vertices of the polygon are in rows 2:6. As you can see I added the first vertice again at the end.
The area, in E2:
=1/2*ABS(SUMPRODUCT(A2:A6,B3:B7)-SUMPRODUCT(B2:B6,A3:A7))
<table style="border-color: rgb(204, 204, 204); border-width: 2px; background: rgb(255, 255, 255) none repeat scroll 0% 0%; border-collapse: collapse; font-family: Arial,Arial; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; font-size: 10pt;" border="1" cellpadding="1"><tbody><tr><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">
</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">A</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">B</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">C</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">D</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">E</th><th style="border-color: rgb(136, 136, 136); border-width: 1px; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" width="30">F</th></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">1</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: center;">X</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: center;">Y</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">1</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: left;">Area</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">7</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">3</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">4</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">3</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">6</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">4</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">6</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">5</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">4</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">7</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right; font-weight: bold;">1</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right; font-weight: bold;">2</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="border-color: rgb(0, 0, 0); border-width: 1px; padding: 0.4em 0.5em 0.25em; background: rgb(153, 204, 255) none repeat scroll 0% 0%; text-align: center; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;">8</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td><td style="border-color: rgb(136, 136, 136); border-width: 1px; padding: 0.4em 0.5em 0.25em; text-align: right;">
</td></tr><tr><td style="background: rgb(153, 204, 255) none repeat scroll 0% 0%; padding-left: 1em; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous;" colspan="7">[Book2]Sheet1</td></tr></tbody></table>