Is a math problem, y 1=k 1x+by2=k2x+b, if y 1 is perpendicular to y2, then k 1*k2=- 1.

In the coordinate system, when two straight lines are perpendicular to each other, the coefficient of the analytical formula of the two straight lines is negative reciprocal, that is, k 1×k2=- 1. It is proved by the direction of the straight lines that vector a= 1, k 1 vector b= 1, and k2 are perpendicular to each other.