Question

设lga+lgb=2lg(a-2b),求a/b的值.

Answer 1

4

左边lga+lgb=lgab

右边2lg(a-2b)=lg(a-2b)2

左边＝右边,

则ab=(a-2b)2

两边除以b2

化简为:a/b=(a/b-2)2

另a/b=x

即x=(x-2)2

x2-5x+4=0;

(x-1)(x-4)=0

x=1或x=4

当x=1时,a-2b=-