3.2 Straight Lines
Obj: To understand slope,
intercepts, and how to write
first degree equations.
Graph the equation
y = 3x - 2
y
∆‫ݕ‬
‫ݕ‬ଶ − ‫ݕ‬ଵ ‫݁ݏ݅ݎ‬
=
=
‫ݔ‬ଶ − ‫ݔ‬ଵ ‫݊ݑݎ‬
∆‫ݔ‬
Y
݉=
Negative slope
X
Positive slope
Vertical line
Slope
Horizontal line
x
}
A, B, and C are
integers, A > 0
y=¾x
First Degree Equations
• A straight line
y = -3x + 5
3x – 4y = 9
Forms:
y = mx + b
y – y1 = m(x – x1)
Ax + By = C
Ax + By + C = 0
Graph 4x + 3y = 12
y = 9x – 23
y
• y = mx + b
2x – 5y = 10
Equations
• Ax + By = C
x
Find the slope.
Vertical Lines
Vertical line through (a, 0)
Slope is undefined (no slope)
Horizontal Lines
• (-4, 8), (-7, 14)
• (6, -7), (0, -7)
• y = 27x + 18
• 8x + 9y = 32
• x=a
• y=b
Horizontal line through (0, b)
Slope is 0
Write an equation of a line
perpendicular to 3x – 5y = 15
passing through the point (-2, 1)
Write the equation of a line.
• What do you need?
• Given: m = - ½ y-intercept 15
• Given: m = ¾ (8, -3)
• Given: (9, -1), (-3, -7)
• Parallel
product of slopes is -1
(opposite reciprocals)
slopes are equal
Parallel and Perpendicular Lines
• Perpendicular
Find the equation of the line
tangent to the circle at the
indicated point.
x2 + y2 = 50; (5, -5)
Objective
To understand slope, intercepts,
and how to write first degree
equations.
Practice.
• Page 203
21 – 45 multiples of three;
AND 58