ABOUT NEGATIVE QUESTIONS
We use negative questions to show surprise, in exclamations and when we expect the listener to agree with us.
Utilizamos la preguntas negativas para demostrar sorpresa, en exclamaciones y cuando esperamos que quien nos escucha esté de acuerdo con nosotros.

1. TO SHOW SURPRISE (Para demostrar sorpresa)

Didn't you hear the bell? I rang it four times.
(¿No escuchaste el timbre? Toqué tres veces.)

2. IN EXCLAMATIONS (En exclamaciones)

Doesn't that house look beautiful! (= that house looks really beautiful)
(¡No sé ve hermosa esa casa! (= esa casa es realmente hermosa)

3. WHEN WE EXPECT THE LISTENER TO AGREE WITH US
    (Cuando esperamos que el oyente esté de acuerdo con nosotros)

"Haven't we met somewhere before?" "Yes, I think we have."
("¿No nos hemos visto antes en alguna parte?" "Sí, creo que sí.")

NOTICE THE MEANING OF YES AND NO IN ANSWERS
TO NEGATIVE QUESTIONS:

Didn't Roberto pass his exams?
Yes. (= Yes, he passed them.)
No. (= No, he didn't pass them.)

NOTICE THE WORD ORDER IN NEGATIVE QUESTIONS WITH WHY...?:

Why didn't you lock the door? (not why you didn't lock)
(¿Por qué no cerraste la puerta con llave?)

Why don't we go out to Harley's restaurant? (not why we don't go)
(¿Por qué no vamos a cenar al restaurante Harley's)

Why can't you help me? (not why you can't help me)
(¿Por qué no me puedes ayudar?)

Why wasn't Claudia invited to the party? (not why Claudia wasn't)
(¿Por qué Claudia no fue invitada? = ¿Por qué no invitaron a Claudia?)