已知(a+2b)/5=(3b-c)/3=(2c-a)/7,求(c-2b)/(3a+2b)的值急

已知(a+2b)/5=(3b-c)/3=(2c-a)/7,求(c-2b)/(3a+2b)的值急
已知(a+2b)/5=(3b-c)/3=(2c-a)/7,求(c-2b)/(3a+2b)的值
急

已知(a+2b)/5=(3b-c)/3=(2c-a)/7,求(c-2b)/(3a+2b)的值急
已知(a+2b)/5=(3b-c)/3=(2c-a)/7,求(c-2b)/(3a+2b)的值
假设 (a+2b)/5=(3b-c)/3=(2c-a)/7 = t
a = 5t - 2b
c = 3b - 3t
带入 2c - a = 7t,6b - 6t - 5t +2b = 7t,8b = 18t,b = 9t/4
如果 t = 0,b = 0 = a = c,分母 3a+2b = 0,分式无意义
如果 t 0
(c-2b)/(3a+2b) = (3b - 3t - 2b)/(15t - 6b + 2b)
= (b - 3t ) / (15t - 4b)
= (9t/4 - 3t) / (15t - 9t)
= (9 -12) / 24
= -3 / 24
= -1/8
菩提本无馨 错误在
(3b-c)/3=(2c-a)/7,则3a=11c-21b
应该是 3a=13c-21b
叶绿之夏 错误在
5c-21b=9b-13c---18c=21b----b=6c/7
应该是 18c = 30b ,b = 3c/5