Math Help - Urgent Help Needed

1. Urgent Help Needed

Hello

Please could somebody explain to me how to solve the following:

Thank you

2. $T = \frac{{1 - e}}
{{1 + e}} = \frac{{2 - (1 + e)}}
{{1 + e}} = \frac{2}
{{1 + e}} - 1.$

So

$T + 1 = \frac{2}
{{1 + e}} \implies 1 + e = \frac{2}
{{T + 1}} \implies e = \frac{2}
{{T + 1}} - 1.$

$\therefore \,\,e = \frac{{1 - T}}
{{1 + T}}\,\blacksquare$