平方差
=(1-2/1)(1+2/1)(1-3/1)(1+3/1)(1-4/1)(1+4/1)(1-5/1)(1+5/1)
=(2/1)(2/3)(3/2)(3/4)(4/3)(4/5)(5/4)(5/6)
中间约分
=(2/1)(5/6)
=5/3
平方差
=(1-2/1)(1+2/1)(1-3/1)(1+3/1)(1-4/1)(1+4/1)(1-5/1)(1+5/1)
=(2/1)(2/3)(3/2)(3/4)(4/3)(4/5)(5/4)(5/6)
中间约分
=(2/1)(5/6)
=5/3