Product of Slope of a line and its perpendicular is -1.
Suppose slope of a line is m1 and its perpendicular is m2.
![m1 * m2 = -1](https://img.qammunity.org/2019/formulas/mathematics/middle-school/ny1nv955pm7ksvwy1dq5qak9e4tx9a1c8c.png)
The general slope intercept form is given by :
![y=mx+b](https://img.qammunity.org/2019/formulas/mathematics/college/hmt7wxoetxgettvoxgzsv2e1z1jn04v2qq.png)
We are given the equation,
![y=-3x+4](https://img.qammunity.org/2019/formulas/mathematics/college/zs603lymalzxr0rjw9dj6b5rjp8f69ot34.png)
Comparing our equation with general slope intercept form , we have
slope (m1) = -3
slope of line perpendicular to it (m2) is given by formula above
![m1 * m2 = -1](https://img.qammunity.org/2019/formulas/mathematics/middle-school/ny1nv955pm7ksvwy1dq5qak9e4tx9a1c8c.png)
plugging m1=-3 in this
![(-3) * m2 = -1](https://img.qammunity.org/2019/formulas/mathematics/middle-school/7in0rbrtc0a4t27bryxv2rx5zxhf425d1v.png)
dividing both sides by -3,
m2 =1/3
So slope of line perpendicular to given line is 1/3.