Answer:
C
Explanation:
a² + b² - 2abcosC = c² ( subtract a² + b² from both sides )
- 2abcosC = c² - a² - b² ( multiply through by - 1 )
2abcosC = a² + b² - c²
a, b, c are the sides opposite vertices A, B, C
here a = 4 , b = 3 , c = 2 , then
a² + b² - c²
= 4² + 3² - 2²
= 16 + 9 - 4
= 25 - 4
= 21