Find the Equation Using Two Points (1,-1) , (2,-2)

$(1, - 1)$ , $(2, - 2)$

Step 1

Use $y = m x + b$ to calculate the equation of the line, where $m$ represents the slope and $b$ represents the y-intercept.

To calculate the equation of the line, use the $y = m x + b$ format.

Step 2

Slope is equal to the change in $y$ over the change in $x$ , or rise over run.

$m = \frac{(change in y)}{(change in x)}$

Step 3

The change in $x$ is equal to the difference in x-coordinates (also called run), and the change in $y$ is equal to the difference in y-coordinates (also called rise).

$m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$

Step 4

Substitute in the values of $x$ and $y$ into the equation to find the slope.

$m = \frac{- 2 - (- 1)}{2 - (1)}$

Step 5

Finding the slope $m$ .

Simplify the numerator.

Multiply $- 1$ by $- 1$ .

$m = \frac{- 2 + 1}{2 - (1)}$

Add $- 2$ and $1$ .

$m = \frac{- 1}{2 - (1)}$

Simplify the denominator.

Multiply $- 1$ by $1$ .

$m = \frac{- 1}{2 - 1}$

Subtract $1$ from $2$ .

$m = \frac{- 1}{1}$

Divide $- 1$ by $1$ .

$m = - 1$

Step 6

Find the value of $b$ using the formula for the equation of a line.

Use the formula for the equation of a line to find $b$ .

$y = m x + b$

Substitute the value of $m$ into the equation.

$y = (- 1) \cdot x + b$

Substitute the value of $x$ into the equation.

$y = (- 1) \cdot (1) + b$

Substitute the value of $y$ into the equation.

$- 1 = (- 1) \cdot (1) + b$

Find the value of $b$ .

Rewrite the equation as $(- 1) \cdot (1) + b = - 1$ .

$(- 1) \cdot (1) + b = - 1$

Multiply $- 1$ by $1$ .

$- 1 + b = - 1$

Move all terms not containing $b$ to the right side of the equation.

Add $1$ to both sides of the equation.

$b = - 1 + 1$

Add $- 1$ and $1$ .

$b = 0$

Step 7

Now that the values of $m$ (slope) and $b$ (y-intercept) are known, substitute them into $y = m x + b$ to find the equation of the line.

$y = - x$

Step 8

Find the Equation Using Two Points (1,-1) , (2,-2)

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