不解方程:2x+y=7/2005,x+3y=2005/8,试求代数式6x^2+21xy+9y^2的值.
问题描述:
不解方程:2x+y=7/2005,x+3y=2005/8,试求代数式6x^2+21xy+9y^2的值.
答
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
答
偷懒吧,这都不会
6x^2+21xy+9y^2
=(x+3y)(6x+3y)
=2005/8 * ( 3*7/2005)
=21/8
答
3(2X+Y)(X+3Y)=6x^2+21xy+9y^2=3×7/2005×2005/8=21/8
答
6x^2+21xy+9y^2=3(2x+y)*(x+3y)=21/8