Question

Find the 7th term of the arithmetic sequence -5x-8,-x-14,3x-20,...

Answer 1

a₁ = -5x-8;  a₂ = -x-14; a₇=?

d = a₂ - a₁
  = x-14 - (-5x-8)
  = -x - 14 + 5x + 8
  = 4x-6

a(n) = a₁ + (n-1)d

a₇ = -5x-8 + (7-1)(4x-6)
    = -5x-8 + 6(4x-6)
    = -5x - 8 + 24x - 36
    = 19x - 44