What is the greatest common factor of 12,18,26

Which sum or difference identity would you use to verify that cos (180° - ∅) = -cos ∅? a. sin (α -β) = sin α cos β – cos α sin β b. cos (α -β) = cos α cos β – sin α sin β c. cos (α -β) = cos α cos β + sin α sin β d. sin (α + β) = sin α cos β + cos α sin β

What is the result of adding the system of equations? 2x+y=4 3x-y=6

Does anyone know how to solve and graph this: 4 + | a + 2 | < 7the only part i don't get is the "4 +"