Two lines that are perpendicular to each other intersect at a right angle, which is 90 degrees. In terms of their slopes, if one line has a slope of \( m_1 \), the slope of the line that is perpendicular to it, \( m_2 \), satisfies the relationship:
\[ m_1 \cdot m_2 = -1 \]
This means that the product of their slopes is -1, indicating that they are oriented in opposite directions in a two-dimensional Cartesian plane.