Day 5

1
Day 5

• Objective Students should be able to
• Find the y intercept when given the slope and a
  point on the line.

2
Find the equation
The slope of a line is 2 A point on the line is
(2,5)

• To find the equation we need
• Slope (given)
• Y intercept
• So far we have this much of our equation
• y2x b
• We need to find the b

3
The Steps

• The slope of a line is 2
• A point on the line is (2,5)
• y 2x b
• 5 2(2) b
• 5 4 b
• -4-4
• 1 b

1. Fill in the given Slope.
2. Substitute the given point for x and y.
3. Solve for b
4. Fill in the y intercept in your equation.

y 2x 1
4
Try One

• Find the equation of a line that passes through
  the point (-2, 4) and has a slope of 4.
• We know this much y 4x b
• Substitute the points (-2, 4) for x and y. Be
  CAREFUL not to switch them. This is a common
  error.

5
Substitute and Solve

• We know
• y 4x b the point (-2, 4) is on the line.

4 4(-2) b 4 -8 b 8 8 12 b
Complete Equation is y 4x 12
6
Practice

• Given - Point on the line is (-3, -1) Slope is 3

y 3x b -1 3(-3) b -1 -9 b 9 9
8 b
y 3x 8
7
Practice

• Given - Point on the line is (6, 8) Slope is 1/2

y 1/2 x b
8 ½(6) b 8 3 b -3-3 5 b
y ½ x 5
8
Practice

• Given - Point on the line is (12, 48) Slope is
  1/4

y ¼ x b
48 ¼ (12) b 48 3 b -3 -3 45 b
Y ¼ x 45
9
What if you just have a line?

• If you have a line, you can find the equation.
• Find the slope of the line using 2 points and the
  slope formula.
• Use one point and the slope you just found to
  find the y - intercept.
• Now you have all you need for the equation!

10
Try One

• First find slope
• (6, 0) and (0, -4)

y 2/3x b 0 2/3(6) b 0 4 b -4 -4 -4
b
y 2/3x - 4
11
Practice Find the Equation

• Find the equation of the line that passes through
  (3,6) and (-2, 5).

• First the Slope using the slope formula
• Then put the slope in the equation
• Substitute one of the points for x and y
• Solve for b

12
Practice

• Your teacher will give you 2 points
• Find the equation