上财的第二版的p25倒数第五行：“thus in our example of a 10 percent increase in the saving rate, output is 0.04(5%) = 0.2% above its previous path after 1 year; is 0.5(5%) = 2.5% above after 18 years;”我没看明白这是怎么得来的，用的是哪个式子或性质退出来的啊？？请教高人帮我解答一下，见笑了！！