1.You are saving for a new car which will cost $14500.You sa

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1.You are saving for a new car which will cost $14500.You save by putting $200 a month into a saving account which gives 0.1%interest a month .After how many months will you be able to afford to buy the car
2.Find the coordinates of the points on the curve with equation y=4x-(16/3)x^3 where the tangents to the curve are parallel to the x-axis .
楼下的高手:
第一题怎么得出结论的?有个关系式吧

【【【公式】】】
S=R(((1+i)^n-1)/i)(1+i)
其中S为14500,r为200,n为要求的月数,i为0.1%,带进去算得出以下结论.
翻译：
1.你想买一辆14500美金的新车,于是你每个月把200块钱存到一个账户里面,这个账户每月底有0.1%的利息.多少个月之后你才有钱买这辆车?
2.在函数 y=4x-(16/3)x^3 中,找正切线与x轴平行的坐标点
1.第一个月开始存200,
月底得 200+200*0.001=200.2
第二个月开始存200,
月底得（200+200.2）+ （200+200.2）*0.001=400.6
第三个月开始存200,
月底得（400.6+200）+ （400.6+200）*0.001=601.2
以此类推最后得出70个月之后,有14508美金,可以买车.
2.方程 y=4x-(16/3)x^3 求正切线与x轴平行的坐标点相当于求这个方程的斜度为0的坐标点.斜率方程为 y'=4-3(16/3)x^2=4-16x^2
把斜率方程设为0 》》》 -16x^2+4=0 >> 16x^2=4>> x^2=1/4
>>> x=正负1/2 >>>当x=正1/2,y=4/3 当 x=负1/2,y=-4/3 >>>
正切线与x轴平行的坐标点为（-1/2,-4/3)和（1/2,4/3)

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