Algebra: A Combined Approach (4th Edition)

$(x+1)^{2}$ - 15(x+1) + 56 = 0 Substitute y = x+1 $y^{2}$ - 15y +56 = 0 (y-8)(y-7) = 0 y = 8 or 7 Since x+1 = 8 or x+1 = 7 x = 7 or 6