应该是：a2+a3=70,
a1+a4=a1+a1q^3=133,
a2+a3=a1q+a1q^2=70,
a1(1+q^3)=133,a1(q+q^2)=70,
(1+q^3)/(q+q^2)=133/70,
133q(q+1)=70(1+q)(1-q+q^2),
q=-1显然不可能,a2+a3=0,
133q=70-70q+70q^2,
70q^2-203q+70=0,q=(203±147)/140,
q=2.5或0.4,a1=8或125
an=8*2.5^(n-1)或125*0.4^(n-1)