Notation. 1.2
Prove that in any arithmetic series in which the first term is a and whose constant
difference is d, the sum of the first n terms is Sn = 12a + (n - 1)d]
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Statement reason 1. δabc is similar to δced. given 2. 3. definition of slope 4. slope of slope of definition of slope 5. slope of × slope of multiplying the slopes 6. slope of × slope of substitution property of equality 7. slope of × slope of simplifying the right side the table contains the proof of the relationship between the slopes of two perpendicular lines. what is the reason for statement 2? a. parallel line segments that meet a common perpendicular line are proportional in length. b. the lengths of vertical and horizontal sides in congruent triangles are in a common ratio. c. trigonometric identities determine the lengths of the legs in a right triangle. d. corresponding side lengths in similar triangles are proportional in length.

4. (10.03 mc) the equation of line cd is y = −2x − 2. write an equation of a line parallel to line cd in slope-intercept form that contains point (4, 5). (4 points) y = −2x + 13 y = negative 1 over 2 x + 7 y = negative 1 over 2 x + 3 − 2x − 3

Given the numbers c = –3 and d = 4, which statement is true? a. |–c| = 3 and |–d| = –4 b. |–c| = 3 and –|d| = –4 c. –|c| = –4 and –|d| = 3 d. |–c| = 3 and –|d| = 4