equation of slope: (y2-y1)/(x2-x1) (-10 - -2) / (a - -1) (-10 + 2) / (a + 1) (-8) / (a + 1)
set this equal to 4 since the slope is given: 4 = -8/(a+1) multiply (a+1) to both sides 4(a+1) = -8 distribute 4a + 4 = -8 subtract 4 from both sides 4a = -12 divide both sides by 4 a = -3
