Answer:
D) 19.5
Step-by-step explanation:
The law of cosines gives you the relation ...
a² = b² + c² - 2bc·cos(A)
Substituting the given values, you have ...
a² = 13² + 11² - 2·13·11·cos(108°) ≈ 378.379
a ≈ √378.379 ≈ 19.452 . . . . take the square root
a ≈ 19.5
