不解方程：2x+y=7/2005,x+3y=2005/8,试求代数式6x^2+21xy+9y^2的值

网友回答

3（2X+Y)(X+3Y)=6x^2+21xy+9y^2=3×7/2005×2005/8＝21/8
======以下答案可供参考======
供参考答案1:
6x^2+21xy+9y^2＝3（2x+y）*（x+3y）＝21/8
供参考答案2:
偷懒吧,这都不会
6x^2+21xy+9y^2
=(x+3y)(6x+3y)
=2005/8 * ( 3*7/2005)
=21/8供参考答案3:
6x^2+21xy+9y^2
=3(2x+y)(x+3y) 代入数据就可以了
你不要去算x y的值 那是陷阱