y=sin²x+­acosx-1/2a­-3/2=1-cos²x+­acosx-1/2a­-3/2≤1,则-cos²x+­acosx-1/2a­-3/2≤0.-(cosx-a/2)²+a²/4-1/2a­-3/2≤0①当a>2时,cosx=1,则y值最大;则sinx=0...