由题意可知
a+b=ac
a+2b=ac^2
即b=a(c-1)
2b=a(c^2-1)
c^2-1=2c-2
c=1(不合题意,舍去)
或a+b=ac^2
a+2b=ac
即b=a(c^2-1)
2b=a(c-1)
c-1=2c^2-2
c=-1/2或c=1(舍去)
所以c=-1/2
由题意可知
a+b=ac
a+2b=ac^2
即b=a(c-1)
2b=a(c^2-1)
c^2-1=2c-2
c=1(不合题意,舍去)
或a+b=ac^2
a+2b=ac
即b=a(c^2-1)
2b=a(c-1)
c-1=2c^2-2
c=-1/2或c=1(舍去)
所以c=-1/2