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Algebra 2
Chapter 2.4bWriting Linear Equations
Target Goals:1. Write an equation of a line parallel or
perpendicular to a given line
Parallel Lines
• Characteristics of PARALLEL lines:– Never cross– Run next to each other forever without crossing– Same steepness– SAME SLOPE!!!
Parallel Lines
Perpendicular Lines
• Characteristics of Perpendicular lines:– Cross– Cross at right angles (90°)– OPPOSITE RECIPROCAL SLOPES!!!
Perpendicular Lines
Parallel vs. Perpendicular • PARALLEL LINES have EQUAL slopes while
PERPENDICULAR LINES have OPPOSITE RECIPROCAL slopes.
• PARALLEL = EQUAL SLOPES• PERPENDICULAR OPPOSITE RECIPROCAL
SLOPES
Ex 1) Write an equation in slope-intercept form of a line that passes through (3, 7) and is parallel to the line with equation 3
54
y x
y mx b
Slope of the given line?
3/4
Slope-intercept form?
37 3
4b
97
4b
974b
28 9
4 4b
19
4b
3 19
4 4y x
37 3
4y x
3 97
4 4y x
3 97
4 4y x
3 9 28
4 4 4y x
3 19
4 4y x
Ex 2) Write an equation in slope-intercept form for the line that passes through (3, -2) that is perpendicular to the line with equation y = -5x + 1
y mx b
Slope of the given line?
-5
Slope-intercept form?
Slope of a perpendicular line?
1/5
12 35
b
325b
325b
10 3
5 5b
13
5b
1 13
5 5y x
12 35
y x
1 325 5
y x 1 3
25 5
y x
1 3 10
5 5 5y x
1 13
5 5y x