Tg(555)=tg(360+15)=tg(15)=0,2679...
1/ctga + cosa/1+sina = 1 / cosa/sina + cosa / 1 + sina = sina/cosa + cosa / 1 + sina = sina + sin^2a + cos^2a / (1 + sina)cosa = sina + 1 / (1 + sina)cosa = 1/cosa
Х(3У-1)-У(Х-3)-2(ХУ-Х+У)=3xy-x-xy+3y-2xy+2x-2y=x+y
(3х+2)(х+3)=(х+2)(2х+3)
3x²+9x+2x+6=2x²+3x+4x+6
3x²+9x+2x-2x²-3x-4x=6-6
x²+4x=0
x(x+4)=0
x=0
или
x+4=0
x=-4
#3
(3а-2)( 9a²+6а+4)=27a³-8
1)11 1/63*9=11*9+1/63=99 9/63=9:9/63:9=99 1/7
2)12 1/35*5=12*5+1/35=60 5/35=5:5/35:5=601/7
3)99 1/7-60 1/7=99-60=39