<s>[INST] Find sum of the roots of quadratic polynomials 
The zeroes of a quadratic polynomial $x^2+ax+b$ are $c$ and $d$ and the zeroes of a quadratic polynomial $x^2+cx+d$ are $a$ and $b$. Find the value of $a+b+c+d$.

The thing doesn't make sense how to use the two equations to get the sum?
Should I use the Vieta's formulas to find it?
 [/INST] Hint You know that
$$x^2 + ax + b = (x-c)(x-d) = x^2 - (c+d)x + cd\\
x^2 + cx + d = (x-a)(x-b) = x^2 - (a+b)x + ab$$
Now compare the coefficients to get four equations.
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