化简【 { a³-8分之a³+2a²+4a}-{a²+a-6分之10}】

[{a³-8分之a³+2a²+4a}-{a²+a-6分之10}]÷[1- { a²-4分之21}]×[a-2分之a+3]
=[{(a-2)(a²+2a+4)分之a(a²+2a+4}-{(a-2)(a+3)分之10}]÷[a²-4分之a²-25]×[a-2分之a+3]
=[(a-2)分之a-(a-2)(a+3)分之10]÷[(a-2)(a+2)分之(a-5)(a+5)]×[(a-2)分之(a+3)]
=[(a-2)(a+3)分之a(a+3)-10]×[(a-5)(a+5)分之(a-2)(a+2)]×[(a-2)分之(a+3)]
=[(a-2)(a+3)分之(a-2)(a+5)]×[(a-5)(a+5)分之(a+2)(a+3)]
=[(a+3)分之(a+5)]×[(a-5)(a+5)分之(a+2)(a+3)]
=(a-5)分之(a+2)第三部到第四部没懂？增么变化的？=[(a-2)(a+3)分之a(a+3)-10]×[(a-5)(a+5)分之(a-2)(a+2)]×[(a-2)分之(a+3)]=[(a-2)(a+3)分之(a²+3a-10)]×[(a-5)(a+5)分之(a-2)(a+2)]×[(a-2)分之(a+3)]=[(a-2)(a+3)分之(a-2)(a+5)]×[(a-5)(a+5)分之(a+2)(a+3)]=[(a-2)(a+3)分之(a²+3a-10)]×[(a-5)(a+5)分之(a-2)(a+2)]×[(a-2)分之(a+3)]=[(a-2)(a+3)分之(a-2)(a+5)]×[(a-5)(a+5)分之(a+2)(a+3)]这两部是怎么变得？约了分也变不出来啊？我约分后是（a²-25）（a-2）分之（a²+3a-10)（a+2）[(a-5)(a+5)分之(a-2)(a+2)]×[(a-2)分之(a+3)]=(a-5)(a+5)(a-2)分之(a-2)(a+2)(a+3) 约分=(a-5)(a+5)分之(a+2)(a+3)