Question 898329
{{{ sin( 225 ) * cos( 90 ) - cos( 225 ) * sin( 90 ) }}}
{{{ cos( 90 ) = 0 }}}
{{{ sin( 90 ) =  1 }}}
The problem reduces to:
{{{ - cos( 225 ) }}}
{{{ -cos( 180 + 45 ) }}}
The cosine is negative in the 3rd quadrant, so
{{{ -( - sqrt(2) / 2 ) }}}
{{{ sqrt(2) / 2 }}}