(1) n^4+4(2) x^5+x+1(2) a^3+2a^2-12a+15注：^表示次方这是老师的作业

(1) n^4+4
=n^4+4n²+4-4n²
=(n²+2)²-4n²
=(n²+2n+2)(n²-2n+2)
(2) x^5+x+1
=x^5-x²+x²+x+1
=x²(x³-1)+(x²+x+1)
=x²(x-1)(x²+x+1)+(x²+x+1)
=(x³-x)(x²+x+1)+(x²+x+1)
=(x³-x+1)(x²+x+1)
(2) a^3+2a^2-12a+15
=a³+5a²-3a²-12a+15
=a²(a+5)-3(a²+4a-5)
=a²(a+5)-3(a+5)(a-1)
=a²(a+5)-(a+5)(3a-3)
=(a²-3a+3)(a+5)