X平方-6X+9分之X平方-4,其中X=3 还有一题是X平方-4X分之X平方-8X+16,其中X=5

X平方-6X+9分之X平方-4
=x(x-6)+1/9(x^2-36)
=x(x-6)+1/9(x+6)(x-6)
=(x-6)[x-1/9(x+6)]
=1/9(x-6)(9x-x-6)
=1/9(x-6)(8x-6)
=2/9(x-6)(4x-3)
=2/9(3-6)(4*3-3)
=2/9*(-3)*9
=-6
X平方-4X分之X平方-8X+16
=X^2-(x-4)^2/4x
=25-(5-4)^2/4*5
=25-1/25
=624/25