解方程1x3/1+3x5/1+5x7/1+…+(2n-1)(2n+1)/1=20/21 急~!
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解方程1x3/1+3x5/1+5x7/1+…+(2n-1)(2n+1)/1=20/21 急~!
解方程1x3/1+3x5/1+5x7/1+…+(2n-1)(2n+1)/1=20/21 急~!
解方程1x3/1+3x5/1+5x7/1+…+(2n-1)(2n+1)/1=20/21 急~!
题目有误,修改为
1x3/1+3x5/1+5x7/1+…+(2n-1)(2n+1)/1=10/21
【1-1/3+1/3-1/8+1/8-1/7+……+1/(2n-1)-1/(2n+1)】÷2=10/21
【1-1/(2n+1)】÷2=10/21
n/(2n+1)=10/21
21n=10(2n+1)
21n=20n+10
n=10
同学下次大的时候要写1/1*3这样就不会有误会了啊。1*2(1-1/3+1/3-1/5+1/5-1/7+.......1/(2n-1)-1/2n+1=1/2(1-1/2n+1)=n/2n+1你的答案是正确的不啊?
要乘以分母数字之差使变形后的式子和原式相等 这是重点
1*2(1-1/3+1/3-1/5+1/5-1/7+.......1/(2n-1)-1/2n+1=1/2(1-1/2n+1)=n/2n+1