Нет действительных решений
1) cos69=cos (90-21)=sin21;
cos79=sin11; cos10+cos11cos21+sin21sin11=cos10+cos (21-11)=2cos10;
2) sin20+sin13cos33-sin33cos13=sin20+sin (13-33)=0;
( 5 1/3 )^7 • ( 3/16 )^8 = ( 16/3 )^7 • ( 16/3 )^ -8 = ( 16/3 ) ^ - 1 = 3/16
Ответ 3/16
1+ctg2x=-1/sin2x
sin2x/sin2x + cos2x/sin2x + 1/ sin2x =0
sin2x+cos2x+1=0
cos^2 x - sin^2 x +2 sinxcosx+ cos^2x + sin^2x=0
2sinxcosx+2cos^2x=0
2cosx(sinx+1)=0
cosx=0
x=П/2 +Пn
sinx=-1
x= -- П/2 +Пn