求助数学题,急!

1.x^2+11xy+18y^2=(x+9)(x+2)
2.(x-y)^2-3(x-y)-40=(x-y-8)(x-y+5)
3.x^4+7x^2-18=(x^2+9)(x^-2)=(x^2+9)(x-根号2）(x+根号2)

这题目不难,不应该依赖别人,要自己做,不然以后考试过不了关的
(x+2y)(x+9y)
(x-y-8)(x-y+5)
(x^2-2)(x^2+9)

1、（x+2y)(x+9y)
2、(x-y+5)(x-y-8)
3、(x^2-2)(x^2+9)

1.(X+2Y)(X+9Y)
2,3这种题目要用换元的方法来解
2.(X-Y-8)(X-Y+5)
3.(X^2-2)(X^2+9)

一，(X+2)(X+9)二，(X-Y-8)(X-Y+5)三，(X^2+9)(X-根号2)(X+根号2)

1.(x+2y)(x+9y)
2.(x-y+5)(x-y-8)
3.?