Margföldun – Æfing 3.5 – Lausnir

  1. 7(x – 1)2 = 7(x2 – 2x + 1) = 7x2 – 14x + 7
  2. (7x – 7)2 = 49x2 – 2·7·7x + 49 = 49x2 – 98x + 49
  3. (x + 5)(x – 5) = x2 – 25 (notum samokaregluna)
  4. (2r + 4)(2r – 4) = 4r2 – 16 (notum samokaregluna)
  5. (3a + 7)(3a – 7) = 9a2 – 49
  6. pb(a + b)(c + b) = pb(ac + ab + bc + b2) = abcp + ab2p + b2cp + pb3
  7. (x + 3)(x + 1)(x – 2) = (x + 3)(x2 – x – 2) = x3 – x2 – 2x + 3x2 – 3x – 6 = x3 + 2x2– 5x – 6
  8. (v2 + 1)(v -1)(v + 1) = (v2 + 1)(v2 – 1) = v4 – 1 (notum samokaregluna tvisvar)