(x^2-5)^2+8(5-x^2)+16
=(x^2-5)^2-8(x^2-5)+16
=(x^2-5-4)^2
=(x^2-9)^2
=(x+3)^2(x-3)^2=(x^2-5-4)^28到哪里去了。a^2-8a+16=(a-4)^2