Example: In Figure 4-21, side b of the triangle equals 97.85 feet, side c equals 106.66 feet, and angle A
equals 73 19' 27". Find side a.
Figure 4-21. Case III
Solution:
Now combine the different parts of the equation.
a2 =b2 + c2 -2 be cos A
a2 = (9574.62 + 11376.36) -5989.63 = 14961.35
When solving for the remaining two unknown angles of the triangle and two sides and the included
angle are known, it is best to use the tangent law in the solution.
Example: In Figure 4-22, page 30, side c of the triangle equals 749.63 feet, side a equals 561.88 feet, and
angle B equals 41 17' 32". Find angle A and angle C.
4-29
EN0591
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