# What is the slope of a line perpendicular to the line with equation y = 4x + 5?

The 2 lines are perpendicular, one to the other, when the product of their slopes is $- 1$.
In this example: $4 \cdot \left(- \frac{1}{4}\right) = - 1.$
Then, the answer is $\left(- \frac{1}{4}\right) .$