To evaluate the expression \( R^2 - \frac{3}{4}r \) when \( r = 3 \), we first need to substitute \( r = 3 \) into the expression:
\[ R^2 - \frac{3}{4}(3) \]
Calculating \( \frac{3}{4}(3) \):
\[ \frac{3 \cdot 3}{4} = \frac{9}{4} \]
Now substitute this back into the equation:
\[ R^2 - \frac{9}{4} \]
Without a specific value for \( R \), we can only express the result as \( R^2 - \frac{9}{4} \). If you have a specific value for \( R \), please provide it, and I can help with further calculations.