Given:
There are given that the cos function:

Explanation:
To find the value, first, we need to use the half-angle formula:
So,
From the half-angle formula:

Then,
Since 105 degrees is the 2nd quadrant so cosine is negative
Then,
By the formula:

Then,
Put the value of cos210 degrees into the above function:
So,

Final answer:
Hence, the value of the cos(105) is shown below:
The slope-point formula:

We have (0, 3) and (-10, 4)
Substitute:

You add $5.38 & $15.95, which equals $21.33. Then subtract $21.33 from $38.12. Your answer is $16.79. That's how much Shane spent on the book.