How can you use 4×7 to find 8×7 find the product

5500 dollars is placed in an account with an annual interest rate of 6.5%. to the nearest tenth of a year, how long will it take for the account value to reach 19700 dollars?

In the 30-60-90 triangle below side s has a length of and side r has a length

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).