The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4.153\\[1 em]x_2 &= -0.903 \end{aligned} $$Step 1:
Combine like terms:
$$ \color{blue}{x^2} + \color{blue}{3x^2} -13x-15 = \color{blue}{4x^2} -13x-15 $$Step 2:
The solutions of $ 4x^2-13x-15 = 0 $ are: $ x = \dfrac{ 13 }{ 8 }-\dfrac{\sqrt{ 409 }}{ 8 } ~ \text{and} ~ x = \dfrac{ 13 }{ 8 }+\dfrac{\sqrt{ 409 }}{ 8 }$.
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