2
ОЗ (1+3x)(1-3x)≠0⇒x≠-1/3 U x≠1/3
12=(1-3x)(1-3x)+(1+3x)(1+3x)
1-6x+9x²+1+6x+9x²=12
18x²=10
x²=5/9
x=-√5/3
x=√5/3
3
ОЗ (1-t)(1+t)≠0⇒t≠1 U t≠-1
t²-3-(t+1)(t+1)=4(1-t)
t²-3-t²-2t-1-4+4t=0
2t=8
t=4
4
ОЗ (y-1)(y+1)≠0⇒y≠1 U y≠1
y²+17-(y-2)(y-1)+5(y+1)=0
y²+17-y²+y+2y-2+5y+5=0
8y=-20
y=-20:8
y=-2,5