Question

数学高手请进！！求助！！选择填空答案！解答题要详细过程

Answer 1

5、C
6、D

（1）a^4-9b^2=(a^2-3b)(a^2+3b)
(2)4(x-y)^2-2(x-y)
=2(x-y)(2x-2y-1)

(3)x^2-2xy-9-y^2
=(x-y)^2-3^2
=(x-y+3)(x-y-3)

(4)y^4+2y^2-24
=(y^2+1)^2-25
=(y^2+6)(y^2-4)
=(y^2+6)(y+2)(y-2)

2
(x+y)^2=9.(x-y)^2=5
x^2+y^2=1/2[(x+y)^2+(x-y)^2]=1/2*14=7
xy=1/4[(x+y)^2-(x-y)^2]=1/4*4=1

Answer 2

5.
a=-2, b=1/2
b/a=-1/4
选C

6.
a^5-a=a(a^4-1)=a(a^2+1)(a^2-1)=a(a-1)(a+1)(a^2+1)
选D