\( \displaystyle y = {x^2 \over 2} - {3 \over 4}\,x + 25 = {1 \over 2}\,x^2 - {3 \over 4}\,x + 25 \)
\( \displaystyle y\,' = 2\cdot {1 \over 2}\,x - {3 \over 4} = x - {3 \over 4} \)