Use an appropriate half-angle formula to find the exact value of the expression. cos(9pi/8)

What is the value with a place of tenths in 907.456 1) 0 2) 6 3) 4 4) 5

Scott harris can invest $7,000 in a 1-year cd that earns interest at an annual rate of 4 percent compounded monthly. the amount per $1.00 is 1.040742. he can also invest $7,000 in a 1-year cd at annual rate of 4 percent compounded quarterly. the amount per $1.00 is 1.040604. what is the difference in the amount of interest earned for each investment? a) $0.96 b) $0.81 c) $0.87 d) $0.88

Can some one me with these questions