Answer:
Full proof below
Step-by-step explanation:

Answer:
8.2
Step-by-step explanation:
Use cosine law:
BC² = 7² + 9² - 2(7)(9)cos(60)
BC² = 67
BC = sqrt (67)
BC = 8.1853
BC = 8.2 (nearest tenth)
-k^2 - (3k - 5n) + 4n....when k = -1 and n = -2
-1^2 - (3(-1) - 5(-2) + 4(-2)
1 - (-3 + 10) + 4(-2)
1 - 7 - 8
-14 <=