Упростите выражение 2cos^2×a/2-cosa-1

1) 2sin(a/2)cos(a/2) / 2 = sin2*(a)2) / 2 = sina / 2 =(1/2)sina.2) cosa / [sin(a/2) - cos(a/2)] =[cos^2(a/2) - sin^2(a/2)] / [sin(a/2 - cos(a/2)] =[cos(a/2) - sin(a/2)]*[cos(a/2)+sin(a/2)] / [sin(a/2) - cos(a/2)]= - sin(a/2) - cos(a/2)