How to calculate right riemann sum from table unequal intervals

Find the sum of the first 8 terms of the following sequence. round to the nearest hundredth if necessary.

Acircle has a circumference of 2 pi cm. which statement about the circumference and area is true? a comparison of the area and circumference is not possible since the area cannot be determined. the numerical values of the circumference and area of the circle are equal. the numerical value of the circumference is greater than the numerical value of the area. the numerical value of the circumference is less than the numerical value of the area.

Express the following as a function of a single angle. cos(60) cos(-20) - sin(60) sin(-20)