10 SYS 37173,"0",-3,15,-3
20 :
30 FOR A=2 TO 0 STEP -0.5
40 : SYS 37173,"+SQR(A*A-0.25*X*X+2*X+2)+1"
50 : SYS 37173,"-SQR(A*A-0.25*X*X+2*X+2)+1"
60 NEXT A
70 :
80 POKE 198,0:WAIT198,1:GETZ$
90 SYS 40211