方程1×2分之x+2×3分之x+……+19×20分之x等于19
求x
急用!
人气:438 ℃ 时间:2019-08-21 15:47:57
解答
1×2分之x+2×3分之x+……+19×20分之x
=x(1-1/2+1/2-1/3+1/3-1/4+------+1/19-1/20)
=x(1-1/20)
=19x/20=19
x=20
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