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Again the trick is to look for the right angles triangles
Here in yellow is the one that we can use for all the jack rafters.
Lets start by calculating the
Jack Rafter Edge Cut
(TOA)
tan of angle Jack Edge Cut = Opposite ÷ Adjacent
tan Jack Edge Cut = ½ span of roof ÷ TL Common
tan Jack edge Cut = 1430 ÷1868
tan Jack Edge Cut = 0.76552
(use inverse tan) Jack Edge Cut = 37.43º
True Length Jack Rafters
(TOA
tan of angle Jack Edge Cut = Opposite ÷ Adjacent
Adjacent = Opposite ÷ tan of angle Jack Edge Cut
the adjacent side is the True Length Jack
So True Length Jack (1) = (1430 - 330) ÷ 0.76552 = 1437mm
and True Length Jack (2) = (1430 - 660) ÷ 0.76552 = 1006mm
also True Length Jack (3) = (1430 - 990) ÷ 0.76552 = 575mm
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