1) tg135 *cos(-300)=tg(90+45) * cos300= -ctg45 * cos(360-60)= -1 *cos60= -1/2
2) 8 *tg7π/3 * tg11π/6= 8 * tg(2π+π/3) * tg(2π-π/6)=8*tgπ/3 * (-tgπ/6)= -8*√3 * √3/3= -8
3) 8 tg150* sin(-300) * cos720= 8 tg(180-30) *(-sin(360-60)) * cos(2*360)=
=8* (-tg30) * sin60 *1=-8 * √3/3 *√3/2= -4
3х=9
х=9:3
х=3
х+у=7
3+у=7
у=7-3
у=5
Ответ: (3;5)
X²-3x-5=11-3x
x²-5=11
x²=11+5
x²=16
x1=4 x2=-4