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我有几个数学题 不过是英文的..我想知道过程 还有方法

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我有几个数学题 不过是英文的..我想知道过程 还有方法
1) The sequence 9,18,27,36,45,45,63.consists of successive multiples of 9.This squence is then altered by multiplying every other term by -1,starting with the first term,to produce the new sequence -9,18,-27,36,-45,54...if the sum of first n terms of this now sequence is 180,determine n.
2)how many five-digit positive integers have the property that the product of their digit is 2000
3) In the diagram,triangle ABC is equilateral and the radius of its inscribed circle is 1.A larger cicrcle is drawn through the vertices of the rectangle ABCDE.what is the diameter of the larger circle.
我有几个数学题 不过是英文的..我想知道过程 还有方法
1、通过观察可以发现,将数列两两一组,会发现后一个比前一个大9,所以用180/9=20,所以共有20组,2个一组,所以n=40
2、2000进行分解得到2000=2^4×5^3,因为5×2=10,已经大于9,所以3个5肯定是单独出现.然后来看2^4,可以有(2、8)(4,4)两种拆分方法,所以就是在5个位置上排这两个数(2+8或4+4),共有20种方法,所以有20个
3、没图没真相,还有长方形怎么会是ABCDE?