1.
x(x+y)(x-y)-x(x+y)^2
=x(x+y)(x-y)-x(x+y)(x+y)
=x(x+y)[(x-y)-(x+y)]
=-2xy(x+y)
=-2×(-1/2)×1
=1
2.
x^4-46x^2+25
=x^4-36x^2-10x^2+25
=(x^4-10x^2+25)-36x^2
=(x^2-5)^2-(6x)^2
=(x^2-5+6x)(x^2-5-6x)
3.
a^2-b^2-c^2-2bc
=a^2-(b+c)^2
=(a+b+c)(a-b-c)0
两边之和大于第三边,a-b-c