AB^2=BC^2
AB^2=(2+3)^2+(1-4)^2=34
BC^2=(-1-2)^2+(a-1)^2=9+(a-1)^2
9+(a-1)^2=34
(a-1)^2=25
1) a-1=-5, a=-4
2)a-1=5, a=6
ОТВЕТ: -4 и 6
AB^2=BC^2
AB^2=(2+3)^2+(1-4)^2=34
BC^2=(-1-2)^2+(a-1)^2=9+(a-1)^2
9+(a-1)^2=34
(a-1)^2=25
1) a-1=-5, a=-4
2)a-1=5, a=6
ОТВЕТ: -4 и 6