Question

Find the value of 2abcosC.

Answer 1

C

Explanation:

Given

a² + b² - 2abcosC = c² ( subtract c² from both sides )

a² + b² - c² - 2abcosC = 0 ( add 2abcosC to both sides )

a² + b² - c² = 2abcosC

Here a = 2, b = 2, c = 1 , then

2² + 2² - 1² = 2abcosC

4 + 4 - 1 = 2abcosC , then

2abcosC = 7 → C

Answer 2

7

Explanation:

a=2

b=2

c=1

2ab cos C=a²+b²-c²=2²+2²-1²=4+4-1=7