1)4х^2-(4х^2-4х+1)=15
4х^2-4х^2+4х-1=15
4х-1=15
4х=15+1=16
х=16:4
х=4
2)9х^2-1=(3х-2)^2
9х^2-1=9х^2-12х+4
9х^2-1-9х^2+12х-4=0
12х-5=0
12х=5
х=5/12
3)(3х+1)^2-(3х-1)^2=11х+1,2
9х^2+6х+1-(9х^2-6х+1)=11х+1,2
9х^2+6х+1-9х^2+6х-1=11х+1,2
12х=11х+1,2
12х-11х+1,2=0
х+1,2=0
х=-1,2