prove that

sin(-420).cos(390) + cos(-660).sin(330) = -1

help plz ... my RHS is coming +1 ... totally confused .. help plz.. as soon as possible !!

 sin(2pie+60).cos 30 + cos(4pie-60) .sin(2pie -30)    {since, pie = 180}

-sin60 .cos 30 +cos60 .(-sin30)

-sin60.cos30 -cos60.sin30

-3/4 -1/4

= -4/4 = -1 

hence proved