3. Warm up
Tell whether the relation is a function.
{(-1, 5), (-3, 2), (2, 0), (1, 2)}
Evaluate: f(x) = 2x2 – 4 when x = -3
Find the slope: (5, -1) and (7, -1)
Tell whether the lines are parallel, perpendicular, or neither.
Line 1: (-1, 6) and (2, 8)
Line 2: (3, 2) and (1, 5)
Yes 14
m = 0
m = 2/3
m = -3/2
perpendicular

4. Writing Equations of Lines

5. Essential Question
How can you find an equation of a line given the slope and the y intercept of the line? Given the slope and a point on the line? Given two points on the line?

6. III. How to Write an Equation of a Line Given m and a point
Write down y = mx + b.
Substitute slope for m and the point (x, y).
Solve for b.
Substitute m and b back into the equation.

7. Write the equation of the line given m and a point
Ex 13: m = 2 Point: (2, 3)
y = mx + b
3 = 2 (2) + b
b = -1
y = 2x – 1

8. Write the equation of the line given m and a point
Ex 14: m = 1/2 Point: (4,-3)
y = mx + b
-3 = 1/2 (4) + b
b = -5
y = ½ x – 5

9. Ex 15: m = -2 Point: (-5, 3) y = mx + b 3 = -2 (-5) + b b = -7
Write the equation of the line given m and a point
Ex 15: m = -2 Point: (-5, 3)
y = mx + b
3 = -2 (-5) + b
b = -7
y = -2x – 7

10. Write the equation of the line given m and a point
Ex: 16
m = 4 (1,4)
y = 4x

11. Write the equation of the line given m and a point
Ex: 17
m = ½ (-1,-2)
y = ½ x – 1 ½

12. Write the equation of the line given m and a point
Ex: 18
m = 2 (0,3)
y = 2x + 3

13. Write the equation of the line given m and a point
Ex: 19
m = 3 (3,0)
y = 3x – 9

14. Write the equation of the line given m and a point
Ex: 20
m = undefined (3,6)
x = 3

15. IV. How to Write an Equation of a Line Given TWO points
Write down y = mx + b.
Use the slope formula to find m.
Pick one of the ordered pairs & substitute slope for m and the point (x, y).
Solve for b.
Substitute m and b into the equation.

16. Equation of a Line - Given 2 points
Ex: (2, 3) (4, 5)
y = mx + b
3 = 1(2) + b
b = 1
y = x + 1

17. Equation of a Line - Given 2 points
Ex: (2, 3) (-4, 15)
y = -2x + 7

18. Equation of a Line - Given 2 points
Ex: (2, 2) (0, 4)
y = -x + 4

19. Equation of a Line - Given 2 points
Ex: 24
(2,3) (1,4)
y = -x + 5

20. Equation of a Line - Given 2 points
Ex: 25
(4,5) (5,2)
y = -3x + 17