9x+10y =1 9x-6y=-15 solve using elimination

The line containing the midpoints of the legs of right triangle abc where a(-5,5), b(1, 1), and c(3, 4) are the vertices.

The total number of dental clinics total for the last 12 months was recorded

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