# Descartes' Rule of Signs

Algebra Level 2

The function $$f(x)=x^4+ax^3+bx^2+cx+d$$ has four positive roots. We are also given that $$(b-a)(a+b)+(d-c)(c+d)=2(ac-bd).$$

What is the value of $$(a+b+c+d)^2?$$

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