#"give random angle values to x such as "-pi,-pi/2,0,pi/2,pi,...#
#"for x="-pi" " rArr" "y=-1/2*cos(-pi)=0.5#
#"for x="-pi/2" " rArr" "y=-1/2*cos(-pi/2)=0#
#"for x="0" " rArr" "y=-1/2*cos(0)=-0.5#
#"for x="pi/2" " rArr" "y=-1/2*cos(pi/2)=0#
#"for x="pi" " rArr" "y=-1/2*cos(pi)=0.5#