a)
-2<= x<= 5 => -4>= -2x >= -10 => img=[-10;-4]
-1< x<=-1/2 => -2>= -2x >= -1 => img=[-2;-1)
-3/2<= x => 3>= -2x => img=[3;+infinit)
5/2<=x => -5>= -2x => img=[-infinit;-5)
-6.10=x => 12.20= -2x => img={12.20}
b)
-2x<=4 => x>=-2
-2x>-2 => x<1
-6<=-2x<=2 => 2>=x>=-1
-2/3<=-2x<6 => 1/3>=x>-3
-1/4<-2x<1/2 => 1/8>=x>=-1/4