ON ERROR GOTO f

SCREEN 12
Xmin = -10
Xmax = 10
Ymin = -10
Ymax = 10
inc = (ABS(Xmax) + ABS(Xmin)) / 640
WINDOW (Xmin, Ymin)-(Xmax, Ymax)
LINE (0, Ymax)-(0, Ymin), 9
LINE (Xmin, 0)-(Xmax, 0), 9
FOR x = Xmin TO Xmax STEP inc * 2
  y = SIN(3 * x) + 4
  IF x <> Xmin THEN LINE (x, y)-(oldx, oldy)
  oldy = y
  oldx = x
f:
  RESUME NEXT
NEXT x