【数学】(1-1/2²)(1-1/3²)(1-1/4²)(1-1/5²)……(1-1/2²)(1-1/3²)(1-1/4²)(1-1/5²)……(1-1/99²)(1-1/100²)
问题描述:
【数学】(1-1/2²)(1-1/3²)(1-1/4²)(1-1/5²)……
(1-1/2²)(1-1/3²)(1-1/4²)(1-1/5²)……(1-1/99²)(1-1/100²)
答
(1-1/2²)(1-1/3²)(1-1/4²)(1-1/5²)……(1-1/99²)(1-1/100²)
=(1+1/2)(1-1/2)(1+1/3)(1-1/3)(1+1/4)(1-1/4)……(1+1/99)(1-1/99)(1+1/100)(1-1/100)
=3/2×1/2×4/3×2/3×5/4×3/4×……100/99×98/99×101/100×99/100
=1/2×101/100
=101/200
答
平方差公式展开,然后化成假分数,规律比较明显啊
答
用平方差
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)……(1-1/100)(1+1/100)
=(1/2)(3/2)(2/3)(4/3)……(99/10)(101/10)
中间约分
=(1/2)(101/100)
=101/200