1.
(a+1)^2-9=0
(a+1+9)(a+1-9)=0
(a+10)(a-8)=0
a=-10或a=8
2.
(81-x^4)/(x^2+9)/(x+3)
=(81-x^4)/[(x^2+9)*(x+3)]
=(9-x^2)(9+x^2)/(x^2+9)*(x+3)
=(9-x^2)/(x+3)
=(3-x)(3+x)/(x+3)
=3-x
3
4x^2=(x-1)^2
4x^2-(x-1)^2=0
[2x-(x-1)][2x+(x-1)]=0
(x+1)(3x-1)=0
x=-1或x=1/3
4a^2+1=4a
4a^2+1-4a=0
(2a-1)^2=0
a=1/2