Python 3, 47 bytes

f=lambda l,i=3:i+1and abs(l[i]-l[i-1])-f(l,i-1)

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Take complex number input. Outputs as Truthy/Falsey swapped. Test cases [from Noodle9][1].

48 bytes

lambda a,b,c,d:A(a-b)+A(c-d)-A(b-c)-A(d-a)
A=abs

Try it online!

Python 3, 47 bytes

f=lambda l,i=3:i+1and abs(l[i]-l[i-1])-f(l,i-1)

Try it online!

Take complex number input. Outputs as Truthy/Falsey swapped. Test cases from Noodle9.

48 bytes

lambda a,b,c,d:A(a-b)+A(c-d)-A(b-c)-A(d-a)
A=abs

Try it online!

Python, 48 bytes

lambda a,b,c,d:A(a-b)+A(c-d)-A(b-c)-A(d-a)
A=abs

Try it online!

Take complex number input. Outputs as Truthy/Falsey swapped. Test cases from Noodle9 .

Python 3, 47 bytes

f=lambda l,i=3:i+1and abs(l[i]-l[i-1])-f(l,i-1)

Try it online!

Take complex number input. Outputs as Truthy/Falsey swapped. Test cases [from Noodle9][1].

48 bytes

lambda a,b,c,d:A(a-b)+A(c-d)-A(b-c)-A(d-a)
A=abs

Try it online!