Question

Find the distance from point A to the given line: A(-1, 7), y=3x How do I solve this?

Answer 1

he formula of a distance between a point (a, b)

and a line Ax + By + C = 0:

$d=\dfrac{|Aa+Bb+C|}{\sqrt{A^2+B^2}}$

We have the point A(-1, 7) → a = -1, b = 7

and the line y = 3x → 3x - y = 0 → A = 3, B = -1, C = 0.

Substitute:

$d=\dfrac{|(3)(-1)+(-1)(7)+0|}{\sqrt{3^2+(-1)^2}}=\dfrac{|-3-7|}{\sqrt{9+1}}=\dfrac{|-10|}{\sqrt{10}}=\dfrac{10\sqrt{10}}{\sqrt{10}\cdot\sqrt{10}}\\\\=\dfrac{10\sqrt{10}}{10}=\sqrt{10}$

Answer: d = √10