第 13 步：我们将计算直线的实际斜率。为此，我们需要上升（y 坐标之间的变化）和运行（x 坐标之间的变化）
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stage.set_axis(100)
stage.create_grid_overlay(10, "grey")
stage.set_background("soccerfield")
ballx = -80
bally = random.randint(-100,100)
# sprite = codesters.Sprite("image", x, y)
ball = codesters.Sprite("soccerball", ballx, bally)
netx = 90
nety = random.randint(-100,100)
# sprite = codesters.Sprite("image", x, y)
net = codesters.Sprite("soccernet", netx, nety)
net.flip_right_left()
#sprite = codesters.Line(x-start, y-start, x-end, y-end, "color")
line = codesters.Line(ballx, bally, netx, nety, "blue")
slopeguess = float(line.ask("What is the slope of this line?"))
rise = nety - bally
