(3a-b+2c)(3a+b-2c)+(b+2c)平方
问题描述：
(3a-b+2c)(3a+b-2c)+(b+2c)平方
答
(3a-b+2c)(3a+b-2c)+(b+2c)^2
=(3a-(b-2c))(3a+b-2c)+(b+2c)^2
=(3a)^2-(b-2c)^2+(b+2c)^2
=9a^2-8bc