When constructing parallel and perpendicular lines, how are the steps similar

Which of the following is the true for f(x) = 5cos

Select the lengths in centimeters that would form a right triangle

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )