已知x+3y=6,求x²+3xy+18y的值

已知x+3y=6,求x²+3xy+18y的值
已知x+3y=6,求x²+3xy+18y的值

已知x+3y=6,求x²+3xy+18y的值
x²+3xy+18y
=x(x+3y)+18y
=6x+18y
=6(6-3y)+18y
=36

已知x+3y=6,求x²+3xy+18y的值
x=6-3y 带入得
36-36y+9y^2+18y-9y^2+|18y
=36

原式=x(x+3y)+18y=6x+18y=6(x+3y)=6x6=36~

由x+3y=6得3y=6-x,所以x²+3xy+18y=x^2+(6-x)x+6(6-x)=36
望采纳，谢谢^_^