b/a=1/2,b/c=2/3,求代数式3a-5c-2b/5a-2c+b

问题描述:

b/a=1/2,b/c=2/3,求代数式3a-5c-2b/5a-2c+b

b/a=1/2,b/c=2/3,求代数式(3a-5c-2b)/(5a-2c+b)
∵b/a=1/2,∴a=2b;∵b/c=2/3,∴b=(2/3)c;于是a=2b=(4/3)c;
故(3a-5c-2b)/(5a-2c+b)=[4c-5c-(4/3)c]/[(20/3)c-2c+(2/3)c]=(4-5-4/3)/(20/3-2+2/3)=-7/16