∵a^2-a=2(b+c)=2b+2c,a+2b=2c-3,sinc:sina=4：√13
∴ c:a=4：√13 c=4a√13/13
∴a^2-a=2b+8a√13/13 (1)
a+2b=8a√13/13-3 (2)
(1)+(2)得：a^2=16a√13/13 -3
∴a=√13或a=3√13/13(舍去,因为代入 b