abc不等于0,且a/b=b/c=c/a
a/b*b/c=a/c=(c/a)^2,a^3=c^3,a=c;
a/b*c/a=c/b=(b/c)^2,c^3=b^3,b=c;
所以a=b=c,
3a+2b+c/a-26-3c
=2b+1-26=2a-25