用平方差公式：
1-1/2²=1²-(1/2)²=(1-1/2)×(1+1/2)=1/2×3/2
1-1/3²=1²-(1/3)²=(1-1/3)×(1+1/3)=2/3×4/3
1-1/4²=1²-(1/4)²=(1-1/4)×(1+1/4)=3/4×5/4
1-1/5²=1²-(1/5)²=(1-1/5)×(1+1/5)=4/5×6/5
1-1/6²=1²-(1/6)²=(1-1/6)×(1+1/6)=5/6×7/6
1-1/7²=1²-(1/7)²=(1-1/7)×(1+1/7)=6/7×8/7
1-1/8²=1²-(1/8)²=(1-1/8)×(1+1/8)=7/8×9/8
1-1/9²=1²-(1/9)²=(1-1/9)×(1+1/9)=8/9×10/9
1-1/10²=1²-(1/10)²=(1-1/10)×(1+1/10)=9/10×11/10
那么
原式=1/2×3/2×2/3×4/3×3/4×5/4×……×9/10×11/10
=1/2×11/10
=11/20