Subtract $ \dfrac{5}{2x^2} $ from $ \dfrac{3}{2} $ to get $ \dfrac{ \color{purple}{ 6x^2-10 } }{ 4x^2 }$.

To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 2x^2 }$ and the second by $\color{blue}{ 2 }$.

$$ \begin{aligned} \frac{3}{2} - \frac{5}{2x^2} & = \frac{ 3 \cdot \color{blue}{ 2x^2 }}{ 2 \cdot \color{blue}{ 2x^2 }} - \frac{ 5 \cdot \color{blue}{ 2 }}{ 2x^2 \cdot \color{blue}{ 2 }} = \\[1ex] &=\frac{ \color{purple}{ 6x^2 } }{ 4x^2 } - \frac{ \color{purple}{ 10 } }{ 4x^2 }=\frac{ \color{purple}{ 6x^2-10 } }{ 4x^2 } \end{aligned} $$