设等差数列首项为a1公差为d
则a2=a1+d; a3=a1+2d; a6=a1+5d;
因为a2,a3,a6成等比数列,
所以 a3*a3=a2*a6;
即(a1+2d)^2=(a1+d)*(a1+5d)
化简得d+2a1=0;
a1=-d/2;
a3=2d-(d/2)=3d/2;
a2=d/2;
q=a3/a2=3
所以公比q=3