已知a:b=c:d=k,求:b分之a+b,d分之c+d,b分之a-b,d分之c-d,b+d分之a+c

a：b=c：d=k a=bk c=dk (a+b)/b=(bk+b)/b=k+1 (c+d)/d=(dk+d)/d=k+1 (a-b)/b=(bk-b)/b=k-1 (c-d)/d=(dk-d)/d=k-1 (a+c)/(b+d)=(bk+dk)/(b+d)=k(b+d)/(b+d)=k