Determine the sign of sin 5pi/4 without using a calculator

Use the elimination method to find the solution to the system of equations. 2x - 3y = -9 -x + 3y = 6

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

Which represents the solution set of the inequality 5x-9 < 21? a. x < 12/5 b. x > 12/5 c. x > 6 d. x < 6