求1/(1*2)+1/(2*3)+1/(3*4)…+1/(N*(N+1))的值,N等于20,要求,按四舍五入精确到小数点后第二位
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求1/(1*2)+1/(2*3)+1/(3*4)…+1/(N*(N+1))的值,N等于20,要求,按四舍五入精确到小数点后第二位
求1/(1*2)+1/(2*3)+1/(3*4)…+1/(N*(N+1))的值,N等于20,要求,按四舍五入精确到小数点后第二位
求1/(1*2)+1/(2*3)+1/(3*4)…+1/(N*(N+1))的值,N等于20,要求,按四舍五入精确到小数点后第二位
N=20
原式=1-1/2+1/2-1/3+1/3-1/4+……+1/20-1/21
=1-1/21
=20/21
约等于0.95
1、
P(x,y)
则PO²-PA²=c
(x²+y²)-[(x-c)²+y²]=c
x²+y²-x²+2cx-c²-y²=c
AO不重合,所以c≠0
两边除以c
2x-c-1=0
2、
第一个是3x²+3y²+9x-3y=0
3x²+3y²+2x+y=0
相减
7x-4y=0
1-1/2+1/2-1/3+1/3-1/4+……+1/20-1/21 1-1/21 1-1/21
约等于0.95