What is the slope of a line perpendicular to the line whose equation is x+3y=-21

Question

What is the slope of a line perpendicular to the line whose equation is x+3y=-21

Answer 1

First Solve for y

1) Subtract x on both sides of the equal sign --> 3y = -21 - x

2) Divide each side by 3 --> y = (-21 - x)/3

3) Simplify by dividing each term by 3 --> y = -21/3 - x/3 --> y = -7 - 1/3 x

Using the slope intercept form y = mx + b we can see the slope is -1/3

The slope of a perpendicular is the reciprocal and the oppisite

The reciprocal and opposite of -1/3 is 3.

So the slope of a perpendicular line is 3!

The end!