Download Point-Slope Form

Point-Slope Form
Algebra 1
Learning Targets
• I can interpret an equation in point-slope form
• I can write an equation in point-slope form
given the correct information
Something to think about…
• You are given two point: (1, 3) (-4, -12)
– For us to write an equation through these points in
slope-intercept (y = ax + b) form we need to know the:
slope
y-intercept
– We can find the slope but the y-intercept can be
difficult.
– There is another form of a linear equation that can
help!!!!
Slope-Intercept Form
• y = ax + b
a = slope
b = y-intercept
Point-Slope Form
• y = y1 + a(x – x1)
a = slope
(x1 , y1) = any
given point
Try one
• You know a line has a slope of 3 and a point
on that line is (6, 10), make an equation in
point slope form.
10 + ____(x
3
6
y = ___
- ____)
y1
a
y = 10 + 3(x – 6)
x1
Try one
• You know a line has a slope of -1/3 and a point
on that line is (-9, -4.5), make an equation in
point slope form.
-9
y =-4.5
___ +-1/3
____(x - ____)
y1
a
y = -4.5 – 1/3(x + 9)
x1
Try one
• You know a line has a slope of 0 and a point
on that line is (7, -2), make an equation in
point slope form.
-2 + ____(x
0
7
y = ___
- ____)
y1
y = -2
a
x1
Examples
1. y = 5 + ½ (x – 2)
Slope: ½
2. y = -4 (x – 1) – 2
Slope: -4
3. y = 2/3 (x + 6) – 8
Slope: 2/3
y = ½x + 4
Point: (2, 5)
y = -4x + 2
Point: (1, -2)
y = 2/3 x – 4
Point: (-6, 2)
Finding Slope
• You are given two points: (-11, 0) (-7, 2)
– Make and equation
Slope = ½
Point = (-11, 0) or (-7, 2)
Y = 0 + ½ (x + 11)
or
y = 2 + ½ (x + 7)