(1-1/2²)(1-三分之一²)(1-1/4²)乘以..乘以（1-1/10²）8a²-2=

(1-1/2²)(1-三分之一²)(1-1/4²)乘以..乘以（1-1/10²）8a²-2=
(1-1/2²)(1-三分之一²)(1-1/4²)乘以..乘以（1-1/10²）
8a²-2=

(1-1/2²)(1-三分之一²)(1-1/4²)乘以..乘以（1-1/10²）8a²-2=
用平方差
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)……(1-1/10)(1+1/10)
=(1/2)(3/2)(2/3)(4/3)……(9/10)(11/10)
中间约分
=(1/2)(11/10)
=11/20

1、=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)……(1-1/10)(1+1/10)
=1/2 × 3/2×2/3 ×4/3×3/4× ……×9/10 ×11/10
=1/2×11/10
=11/20

8a²-2
=2(4a²-1)
=2(2a+1)(2a-1)

原式=(1/2 *3/2)*(2/3*4/3)*(3/4*5/4)*……*(9/10*11/10)
=1/2 *11/10
=11/20
解毕。