(x - a)
(x - 1) and (x + 3)
a = 1
a = -3
W(x)=x^3-ax^2-13x+b
\left \{ {{W(1)=0} \atop {W(-3)=0}} \right.
\left \{ {{1-a\cdot 1-13\cdot 1+b=0} \atop {(-3)^3-a\cdot (-3)^2-13\cdot (-3)+b=0}} \right.
\left \{ {{-12-a+b=0} \atop {-27-9a+39+b=0}} \right.
\left \{ {{-a+b=12} \atop {-9a+b=-12 \ |*(-1)}} \right.
\left \{ {{-a+b=12} \atop {9a-b=12}} \right.
8a=24 \ |:8\\\\ a=3
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-a+b=12\\\\ -3+b=12\\\\ 3+b=12 \\\\ b = 15
Answer:
\left \{ {{a=3} \atop {b=15}} \right.