Civil Engineering Reference
In-Depth Information
B
C
A
RAFTER RUN 18 FT
Figure 5-69 Trigonometric ratios may be used to determine
the lengths of rafters for a roof.
Table 5-26 Roof Pitches in Degrees and Minutes
(Measured from the Horizontal)
Pitch
Sine
Cosine
Tangent
4
◦
46
12
×
1
=
0.083098
0.996541
0.083386
9
◦
28
12
×
2
=
0.164474
0.986381
0.166745
14
◦
2
12
×
3
=
0.242486
0.970155
0.249946
18
◦
26
12
×
4
=
0.316201
0.948692
0.333302
22
◦
37
12
×
5
=
0.384564
0.923098
0.416601
26
◦
34
12
×
6
=
0.444635
0.895712
0.496404
×
=
30
◦
15
12
7
0.503774
0.863836
0.583183
×
=
33
◦
41
12
8
0.554602
0.832115
0.666497
12
×
9
=
36
◦
53
0.600188
0.799859
0.750366
12
×
10
=
39
◦
46
0.639663
0.768656
0.832183
12
×
11
=
42
◦
31
0.675805
0.737081
0.916866
12
×
12
=
45
◦
00
0.707107
0.707107
1.000000
main trigonometric ratios (sine, cosine, and tangent) are provided
for each pitch.
Other typical examples of how trigonometric ratios can aid car-
penters are shown in the following problems.
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