A line passes through (9, –9) and (10, –5).

a. Write an equation for the line in point-slope form.
b. Rewrite the equation in standard form using integers.

y + 9 = 4(x – 9); –4x + y = –45

y – 9 = 4(x – 9); –4x + y = 45

y + 9 = 4(x + 9); –4x + y = –45

y – 9 = 4(x + 9); –4x + y = 45

1 answer

Let's solve this step by step.

Step 1: Find the slope of the line

To find the slope of the line that passes through the points (9, -9) and (10, -5), we use the slope formula:

\[ m = \frac{y_2 - y_1}{x_2 - x_1} \]

Substituting in the coordinates:

\[ m = \frac{-5 - (-9)}{10 - 9} = \frac{-5 + 9}{1} = \frac{4}{1} = 4 \]

Step 2: Write the equation in point-slope form

The point-slope form of a line is given by:

\[ y - y_1 = m(x - x_1) \]

Using the point (9, -9) and the slope \( m = 4 \):

\[ y - (-9) = 4(x - 9) \]

Which simplifies to:

\[ y + 9 = 4(x - 9) \]

So, the equation in point-slope form is:

\[ y + 9 = 4(x - 9) \]

Step 3: Rewrite the equation in standard form

The standard form of a linear equation is \( Ax + By = C \), where A, B, and C are integers.

Starting from our point-slope equation:

\[ y + 9 = 4(x - 9) \]

Distributing the 4:

\[ y + 9 = 4x - 36 \]

Next, we will subtract \(4x\) from both sides:

\[ -4x + y + 9 = -36 \]

Now, we will subtract 9 from both sides:

\[ -4x + y = -36 - 9 \] \[ -4x + y = -45 \]

To make the coefficient of \(x\) positive, we can multiply the entire equation by -1:

\[ 4x - y = 45 \]

So, the standard form of the equation is:

\[ -4x + y = -45 \]

Review the Options

The correct answer options are:

  1. \(y + 9 = 4(x - 9)\); \(-4x + y = -45\)

This matches our found point-slope and standard forms.

So the final answer is:

Option: \(y + 9 = 4(x - 9); -4x + y = -45\).