Question

What is an equation of the line that passes through the point (-4,-6) and is perpendicular to the line 4x+5y=25

Answer 1

Answer:

$y = \frac{5}{4} x - 1$

Step-by-step explanation:

The equation of a line is usually written in the form of y=mx+c, where m is its gradient and c is its y-intercept.

First rewrite the equation of the given line in the form of y=mx +c.

4x+5y=25

5y= -4x +25

$y = - \frac{4}{5} x + 5$

The gradient of the given line is $- \frac{4}{5}$

The product of the gradient of perpendicular lines is -1.

$( - \frac{4}{5} )(gradient \: of \: line) = - 1 \\ gradient \: of \: line = - 1 \div ( - \frac{4}{5} ) \\ gradient \: of \: line = \frac{5}{4}$

Thus, m= $\frac{5}{4}$

$y = \frac{5}{4} x + c$

Substitute a coordinate to find c.

When x= -4, y= -6,

$- 6 = \frac{5}{4} ( - 4) + c \\ - 6 = - 5 + c \\ c = 5 - 6 \\ c = - 1$

Hence, the equation of the line is

$y = \frac{5}{4} x - 1$