B- 1/2 the books are science books. You have to add the two fractions and subtract that from one.
The equation would be like this:
Hoped I helped
Answer:

Step-by-step explanation:
we know that

Remember the identity

step 1
Find the value of 
we have that
The angle alpha lie on the III Quadrant
so
The values of sine and cosine are negative

Find the value of sine

substitute




step 2
Find the value of 
we have that
The angle beta lie on the IV Quadrant
so
The value of the cosine is positive and the value of the sine is negative

Find the value of cosine

substitute




step 3
Find cos (α + β)

we have




substitute



The third equation is correct. The easiest way to solve a problem like this is to plug the x-values from the chart into the equations and see which one equals the y-value in the chart.