axyb成等差数列2x=a+y 12y=x+b21式+2式得2x+2y=a+y+x+bx+y=a+b使amnb成等比数列m^2=anm^2/n=a1n^2=mbn^2/m=b21式+2式得m^2/n+n^2/m=a+b=x+ym^2/n+n^2/m=...