Expression 3: sine left parenthesis, left parenthesis, "x" cos "a" negative "y" sin "a" , right parenthesis pi , right parenthesis sine left parenthesis, left parenthesis, "x" sin "a" plus "y" cos "a" , right parenthesis pi , right parenthesis equals 0sinxcosa−ysinaπsinxsina+ycosaπ=0