Law of cosines: a2 = b2 + c2 – 2bccos(a)

which equation correctly uses the law of cosines to solve for the missing side length of pqr?

62 = p2 + 82 – 2(p)(8)cos(39°)
p2 = 62 + 82 – 2(6)(8)cos(39°)
82 = 62 + p2 – 2(6)(p)cos(39°)
p2 = 62 + 62 – 2(6)(6)cos(39°)

One cell phone plan charges $20 per month plus $0.15 per minute used. a second cell phone plan charges $35 per month plus $0.10 per minute used. write and solve an equation to find the number of minutes you must talk to have the same cost for both calling plans.