The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= \dfrac{ 3 }{ 4 }\\[1 em]x_2 &= -\dfrac{ 3 }{ 4 } \end{aligned} $$Step 1:
Get rid of fractions by multipling equation by $ \color{blue}{ 16 } $.
$$ \begin{aligned} x^2-\frac{9}{16} & = 0 ~~~ / \cdot \color{blue}{ 16 } \\[1 em] 16x^2-9 & = 0 \end{aligned} $$Step 2:
The solutions of $ 16x^2-9 = 0 $ are: $ x = -\dfrac{ 3 }{ 4 } ~ \text{and} ~ x = \dfrac{ 3 }{ 4 }$.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.