cos(-9п)+2sin(-49п/6)-ctg(-21п/4)

9π=8π+π49π/6=8*6π/6+π/6=8*π+π/6=4*2π+π/621π/4=20*π/4+π/4=5π+π/4cos(π)-2sin(π/6)+ctg(π/4)= -1-2*1/2+1=-1-1+1= -1