Answer:

Explanation:
step 1
Find cos α
we know that

we have

substitute




Remember that Angle α lies in quadrant II
so
sec α is negative

Find the value of cos α

so

step 2
Find sin α
we know that


we have


substitute


step 3
Find sin β
we know that

we have

substitute





Remember that
Angle β lies in quadrant IV
so
sin β is negative

step 4
Find cos(α−β)
we know that

we have




substitute the given values


