a) -19a: (-19a); б) -45b: (-15b); в) -100cd: (20cd); г) 18dy: (6dy).

a) -19a ∶ (-19a) = (−19 ∶ (−19)) × (a ∶ a) = 1 ∙ 1 = 1

б) -45b ∶ (-15b) = (−45 ∶ (−15)) × (b ∶ b) = 3 ∙ 1 = 3

в) −100cd ∶ (20cd) = (−100 ∶ 20) × (c ∶ c) × (d ∶ d) = −5 ∙ 1 ∙ 1 = −5

г) 18dy ∶ (6dy) = (18 ∶ 6) × (d ∶ d) × (y ∶ y) = 3 ∙ 1 ∙ 1 = 3

Ответ: a) 1; б) 3; в) -5; г) 3