def drawMaxAndMinPoints(pointer, xo, yo, ratio, xmin, xmax, expr):
    pointer.up()
    pointer.goto(xo, yo)
    pointer.down()
    y_coordinates = []
    maxValue = 0
    minValue = 0
    x = 0
    while x <= xmax:
        y = eval(expr)
        y_coordinates.append(y)
        screenX, screenY = screenCoor(xo, yo, ratio, x, y)
        x += 0.5
        if y > maxValue:
            maxValue = y
            pointer.color("purple")
            drawCircle(pointer, screenX, screenY)
        if y < minValue:
            minValue = y
            pointer.color("orange")
            drawCircle(pointer, screenX, screenY)
    y_coordinates = []
    x = 0
    while x >= xmin:
        y = eval(expr)
        y_coordinates.append(y)
        screenX, screenY = screenCoor(xo, yo, ratio, x, y)
        x -= 0.5
        if y > maxValue:
            maxValue = y
            pointer.color("purple")
            drawCircle(pointer, screenX, screenY)
        if y < minValue:
            minValue = y
            pointer.color("orange")
            drawCircle(pointer, screenX, screenY)
    pass