# Red complex 1

Algebra Level 3

Let $$f( x ) ={ x }^{ 4 }+{ ax }^{ 3 }+{ bx }^{ 2 }+{ cx }+d$$ be a polynomial with all real roots.

If $$| f(i) | = 1$$, where $$i =\sqrt{-1}$$, find $$a+b-c+d$$.

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