2x-3x-10x>1/5+1/5
-11x>2/5
x<-2/5:11
x<-2/55
x∈(-∞;-2/55)
1)x=2-y
2)(2-y)y=-8
2y-y²+8=0
-y²+2y+8=0
y²-2y-8=0
y1+y2=2
y1•y2= -8
y1=4 y2= -2
3) x1=2-4=-2
x2=2+2=4
f(u)=3u-u³
f(1)=3*1-1³=3-1=2
f(a)=3a-a³
f(a+1)=3(a+1)-(a+1)³=3a+3-(a³+3a²+3a+1)=3a+3-a³-3a²-3a-1= -a³-3a²+2
f(a-1)=3(a-1)-(a-1)³=3a-3-(a³-3a²+3a-1)=3a-3-a³+3a²-3a+1= -a³+3a²-2
2f(2a)=2(3*2a-(2a)³)=2(6a-8a³)=12a-16a³
f(a)+f(-a)=3a-a³+(-3a-(-a)³)=3a-a³-3a+a³=0