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Warm up

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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

perpendicular

m = 2/3

m = -3/2

Writing Equations of Lines

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?

1. Write down y = mx + b

2. Substituteslope for m and y-intercept for b.

3. Simplify the equation

Ex. 1 Slope is -5 and y-intercept is 2

y = -5x + 2

Ex. 2 Slope is -1/2 and y-intercept is -2

y = -½x – 2

Ex. 3 Slope is 0 and y-intercept is 3

y = 3

Ex. 4 Slope is 1/3 and y-intercept is 0

Write down y = mx + b

Use any 2 “good” points on the graph to find the slope, m.

Find the y-intercept on the graph, b.

Substituteslope for m and y-int for b into the equation y = mx + b.

y = -3x + 2

y = 2x

y = 3

x = - 6

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 y = mx + b.

Ex 10: m = 2Point: (2, 3)

y = mx + b

3 = 2 (2) + b

b = -1

y = 2x – 1

Ex: 11

m = ½ (-1,-2)

y = ½ x – 3/2

Ex: 12

m = 0 (3, -2)

y = -2

Ex: 13

m = undefined (3,6)

x = 3