-8k - 8(-8k + 6) = -8k + 64k - 48 = 56k - 48
It's a value you should probably memorize:

You can derive it using some trigonometric identities, other known values of cosine, and properties of the cosine function. For example, using the double angle identity for cosine:

If
, then

and you probably know that
, so

When we take the square root, we should take the positive root because
whenever
:

Answer:
The persons speed is 7 miles per hour.
Answer:5
Step-by-step explanation:5