2 of 3 added 195 characters in body

Swift 3, 55 bytes

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

Full 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])}

Full Test Suite.