Question

Find the equation of line b described below, in slope-intercept form

Answer 1

Given:

Line a is perpendicular to line b .

Line a passes through the points (1,-8) and (9,-12) .

Line b passes through the point (-8, -16).

To find:

The equation of b.

Solution:

Line a passes through the points (1,-8) and (9,-12) . So, slope of line a is

$m=\dfrac{y_2-y_1}{x_2-x_1}$

$m_a=\dfrac{-12-(-8)}{9-1}$

$m_a=\dfrac{-12+8}{8}$

$m_a=\dfrac{-4}{8}$

$m_a=-\dfrac{1}{2}$

Product of slopes of two perpendicular lines is -1.

$m_a\times a_b=-1$

$-\dfrac{1}{2}\times a_b=-1$

$b=2$

Slope of line b is 2.

If a line passing through a point $(x_1,y_1)$ with slope m, then equation of line is

$y-y_1=m(x-x_1)$

Line b passing through (-8,-16) with slope 2. So, equation of line b is

$y-(-16)=2(x-(-8))$

$y+16=2(x+8)$

$y+16=2x+16$

Subtract 16  from both sides.

$y=2x$

Therefore, the equation of line b is $y=2x$.