The law of cosines is a² + b² - 2abcosC = c². Find the value of 2abcosC.
A. 20
B. 40
C. 37
D. -40

Answer:
C
Step-by-step explanation:
a = 4
b = 5
c = 2
C = arccos((a² + b² - c²) / 2ab)
C = arccos((16 + 25 - 4) / 2(4)(5))
C = arccos(37 / 40)
C = 22.33°
2abcosC
2(4)(5)cos(22.33)
40(0.925)
37