Answer:
C) 
Step-by-step explanation:
By the cos double angle formula, we know 
Substituting 
into the formula, we get
.
The answer is C.
G=b-ca
Subtract b from both sides
G-b=-ca
Divide by -c
(G-b)/-c=a
I hope this Helps!
I'm sorry I'm too lazy to read all of that. However, I did get the main point. The river was going at 3 mph. Since he wanted to travel 10 miles upstream and downstream, you would have to subtract 20 by 3. This would mean he was going at a speed of 17 mph.
Sometimes system outputs are limited because the amount of the necessary information that is perceived in the system .
