3 of 3 added 169 characters in body

Swift 3, 55 bytes

Note that I declared the variable t because the expression would be too complex to be solved in reasonable time otherwise (Swift's fault!).

func f(a:Int,b:Int,c:Int){let t=c-2*a;print(t*t<8*c*b)}

Test Suite.

or 55 bytes, exact closure equivalent (I need the last part because it is a complex construct):

{let t=$2-2*$0;return t*t<8*$2*$1}as(Int,Int,Int)->Bool

Test Suite.

Swift 3, 57 bytes

func f(a:[Int]){let t=a[2]-2*a[0];print(t*t<8*a[2]*a[1])}

Test Suite.