∵a+b分之c等于b+c分之a等于a+c分之b等于k∴c=ak+bk ①a=bk+ck ②b=ak+ck ③①+②得：a+c=ak+2bk+cka+c-(a+c)*k=2bk(a+c)(1-k)=2bka+c=2bk/(1-k) ④④代人③得b=k*2bk/(1-k)1-k=2k²2k²+k-1=0(2k-1)(k+1)=0...