Find equation of line that passes through point (1,-2) & is perpendicular to

Question

Find equation of line that passes through point (1,-2) & is perpendicular to X + 5y = 2015

Answer 1

Nataline,

 

If the equation of line that passes through point (1,-2) & is perpendicular to X + 5y = 2015 has a slope m1 then the equation of the line X + 5y = 2015 has a slope -1/m1.

In other words, the slope of these perpendicular lines are the negative reciprocal of each other.

You know the slope of X + 5y = 2015. 5y = -x + 2015 <=> y = -1/5x - 2015/5

If -1/m1=-1/5 then m1 - the slope of the perpendicular line - is 5.

=> y = 5x + b is the equation of that line.

Now you have to find b using the point (1,-2), which the line of that equation passes through. 

-2=5(1) + b => b = -7

∴ y = 5x -7