Answer:
Length of a is 6.3
Step-by-step explanation:
Given: b = 3 , c = 9 and ∠A = 21°
To find: value of a.
We use law of cosines.
The law of cosines is used for calculating one side of a triangle when the angle opposite and the other two sides are known.
a² = b² + c² - 2bc × cos A
a² = 3² + 9² - 2 × 3 × 9 × cos(21)
a² = 9 + 81 - 54 × 0.93
a² = 39.78
a = √39.78
a = 6.307
a = 6.3
Therefore, length of a is 6.3
