Let the Vertices of the Δ be A , B , and C
We will follow the Usual Notation for Δ A B C , e.g., the side
opposite to the Vertex A will be denoted by a , m ∠ A = A , etc.
In this notation, let us assume that,
a = 32 , b = 35 , & , C = 120 ° & we have to find c
Using Cosine-Rule for Δ A B C , we have,
c²= a²+b² - 2 ab cos C = 32 ²+35² - 2 x 32 x 35 x cos 120° =
1024 + 1225 − 2240 cos ( 180 °− 60 °) = 2249 - 2240(-cos 60°)
2249+ 2240 (1/2)= 2249 + 1120= 3369
Answer: C= √3369 is about 58.04
Answer: 58.043087 (approximate)
===================================================
Explanation:
Refer to the diagram below. We can use the law of cosines to solve for c
c^2 = a^2 + b^2 - 2*a*b*cos(C)
c^2 = 32^2 + 35^2 - 2*32*35*cos(120)
c^2 = 3369
c = sqrt(3369)
c = 58.043087 which is approximate
Round this value however you need to.
