Question

Consider the line y = 7x-9.

Answer 1

$y = \frac{-1}{7}x -\frac{8}{7}$ is the equation of the line that is perpendicular to this line and passes through the point (6, -2)

y = 7x - 44 equation of the line that is parallel to this line and passes through the point (6, -2)

Solution:

Given that line is:

y = 7x - 9

The equation of line in slope intercept form is given as:

y = mx + b ------ eqn 1

Where, "m" is the slope of line and "b" is the y intercept

On comparing eqn 1 with y = 7x - 9 we get,

m = 7

Find the equation of the line that is perpendicular to this line and passes through the point (6, -2)

We know that,

Product of slope of a line and slope of line perpendicular to given is always -1

Therefore,

$7 \times \text{ slope of line perpendicular to it } = -1\\\\\text{ slope of line perpendicular to it } = \frac{-1}{7}$

Now find the equation of line:

$\text{ Substitute } m = \frac{-1}{7} \text{ and } (x, y) = (6, -2) \text{ in eqn 1}$

$-2 = \frac{-1}{7} \times 6 + b\\\\-2 = \frac{-6}{7} + b\\\\b = -2+\frac{6}{7}\\\\b = \frac{-14+6}{7}\\\\b = \frac{-8}{7}$

$\text{Substitute } m = \frac{-1}{7} \text{ and } b = \frac{-8}{7} \text{ in eqn 1}\\\\y = \frac{-1}{7}x -\frac{8}{7}$

Thus the equation of line perpendicular to given line is found

Find the equation of the line that is parallel to this line and passes through the point (6, -2)

Slopes of parallel lines are equal

Therefore,  m = 7

Substitute m = 7 and (x, y) = (6, -2) in eqn 1

-2 = 7(6) + b

-2 = 42 + b

b = -44

Substitute m = 7 and b = -44 in eqn 1

y = 7x - 44

Thus equation of line parallel to given line is found