Point- slope equation of a line
We know that the point-slope formula is given by:
y − y₁=m(x − x₁)
where the terms: m, y₁ and x₁ are numbers.
Given that the line passes through a given points we have that:
m is the slope of the line
y₁ is the y value of that given point
x₁ is the x value of that given point
Finding the slope
We want to find the slope m, having that
(x₁, y₁) = (-18, -2)
(x₂, y₂) = (9, 10)
The slope is always a rate of change. It is:
m = Δy/Δx,
where Δ means "change"
Step 1: finding the change of each term x and y
Δy = change of y = y₂ - y₁
Δy = 10 - (-2) = 12
Δx = change of x = x₂ - x₁
Δx = 9 - (-18) = 27
Step 2: dividing the found quantities
Then
m = Δy/Δx = 12/27
m = 4/9
Step 3: replacing in the equation
Using the equation, we have that
y − y₁ = m(x − x₁)
replacing m:
y − y₁= 4/9(x − x₁)
Step 4: replacing each point
For the first point: (-18, -2)
We have that (x₁, y₁) = (-18, -2)
since the equation is
y − y₁ = 4/9(x − x₁)
replacing each term for each number of the given coordinate
y − (-2) = 4/9(x − (-18))
y + 2 = 4/9(x + 18)
Equation: y + 2 = 4/9(x + 18)
For the second point: (9, 10)
We have that (x₂, y₂) = (9, 10)
since the equation is
y − y₂ = 4/9(x − x₂)
replacing each term for each number of the given coordinate
y − (10) = 4/9(x − (9))
y - 10 = 4/9(x - 9)
Equation: y - 10 = 4/9(x - 9)