Решение задания приложено
1) Cos5π/3 = Cos(2π - π/3) = Cosπ/3 = 1/2
2) tg(- 5π/6) = - tg(π - π/6) = tgπ/6 = 1/√3 = √3/3
3) tgπ*ctgπ/4 + Cosπ/2*Sin(-2π/3) = 0*1- 0*Sin2π/3 = 0
4) Sin150° - Cos720° + tg225° = Sin(180 - 30) - Cos(2*360 +0) + tg(270 - 45) =
= Sin30° - Cos0 + ctg45°= 1/2 - 1 + 1 = 1/2 = 0,5
6(y-z)/14x(z-y)= -6(z-y)/14x(z-y)= -3/7x
X²-6x=14x-18-x²
x²+x²-6x-14x+18=0
2x²-20x+18=0/÷2
x²-10x+9=0
a+b+c=0
1-10+9=0
x1=1
x2=9