Question 985310
Rewrite the LHS as 

{{{(1 - Sin A + Cos A)(1 - Sin A + Cos A) }}}

Now Multiply Thru

{{{1 - Sin A + Cos A - Sin A + Sin^2A - Sin A Cos A + Cos A - Sin A Cos A + Cos^2A }}}

Now all that is left is to collect like terms 

{{{1 - 2Sin A + 2Cos A - 2SinA Cos A + (Sin^2A + Cos^2A) }}}

We now end up with 

{{{2 - 2Sin A + 2Cos A - 2SinACosA }}}

Now you can either do Factoring By grouping on the previous expression or you can simply expand the RHS of the equation and the two parts are EQUAL with the 2 Factored out of the LHS

QED