Name the property: -2 + (10 + 1) = (-2 + 10) + 1

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.

Asystem of linear equations contains two equations with the same slope. select all of the correct statements. i a. the system may have two solutions. - b. the system may have infinitely many solutions. c. the system may have one solution. o d. the system may have no solution. submit

The sum of the speeds of two trains is 720.2 mph. if the speed of the first train is 7.8 mph faster than the second train, find the speeds of each.