证明:
由定义,(a*b)*c=[(a+b)/(1+ab)]*c
=[(a+b)/(1+ab)+c]/[1+(a+b)c/(1+ab)]
=(a+b+c+abc)/(1+ab+ac+bc)
a*(b*c)=a*[(c+b)/(1+cb)]
=[a+(c+b)/(1+cb)]/[1+a(c+b)/(1+cb)]
=(a+b+c+abc)/(1+ab+ac+bc)
所以(a*b)*c=a*(b*c)
证明:
由定义,(a*b)*c=[(a+b)/(1+ab)]*c
=[(a+b)/(1+ab)+c]/[1+(a+b)c/(1+ab)]
=(a+b+c+abc)/(1+ab+ac+bc)
a*(b*c)=a*[(c+b)/(1+cb)]
=[a+(c+b)/(1+cb)]/[1+a(c+b)/(1+cb)]
=(a+b+c+abc)/(1+ab+ac+bc)
所以(a*b)*c=a*(b*c)