I due prezzi sono uguali.

Because i due prezzi means the two prices specifically.

• due prezzi = two prices in a general or indefinite sense
• i due prezzi = the two prices, referring to two specific prices already known from the context

So the article i adds definiteness, just like the in English.

Because prezzi is a masculine plural noun, and its plural definite article is i.

Here is the pattern:

• il prezzo = the price
• i prezzi = the prices

So:

• i due prezzi = the two prices

Because prezzo is singular, and prezzi is plural.

Many masculine Italian nouns ending in -o form the plural in -i:

• prezzo → prezzi
• libro → libri
• ragazzo → ragazzi

So i due prezzi uses the plural because there are two prices.

No. Due is normally invariable, so it stays the same regardless of gender.

For example:

• due prezzi = two prices
• due case = two houses
• due amici = two friends
• due amiche = two female friends

So you do not change due to match the noun.

Because the subject is plural: i due prezzi.

The verb essere must agree with the subject:

• il prezzo è uguale = the price is the same
• i prezzi sono uguali = the prices are the same

Since there are two prices, Italian uses the plural verb sono.

Because uguali is the plural form of the adjective.

Italian adjectives usually agree with the noun they describe in number, and often in gender too.

Here:

• prezzi = plural
• so the adjective must also be plural: uguali

Compare:

• il prezzo è uguale = the price is the same
• i prezzi sono uguali = the prices are the same

A useful detail: uguale has the same form for masculine and feminine singular, and uguali for masculine and feminine plural.

It can mean both, depending on context.

In a sentence like I due prezzi sono uguali, English would often say:

• The two prices are the same
• or The two prices are equal

In everyday usage, uguale very often corresponds to the same.

No, that is not natural here.

The normal structure is:

• I due prezzi sono uguali

This follows the common pattern:

article + number + noun + verb + adjective

So:

• i due prezzi = the two prices
• sono uguali = are the same / are equal

Normally, no. In standard Italian, numbers usually come before the noun:

• due prezzi
• i due prezzi

So i prezzi due would not be the normal way to say it.

Not always. It depends on whether you mean two in general or the two specifically.

• Due prezzi sono uguali = Two prices are the same / Two prices are equal
• I due prezzi sono uguali = The two prices are the same

So the article is used when the noun phrase is definite.

Yes, in some contexts that is possible, but it is not exactly the same nuance.

• uguali = equal / the same
• gli stessi = the same ones / identical ones

In many situations they are close in meaning, but uguali is a very straightforward and natural choice for comparing prices.

It is pronounced roughly like PRET-tsee.

A couple of useful pronunciation points:

• zz is pronounced as a strong ts or dz sound depending on the word; in prezzi, it is commonly like ts
• the i at the end is clearly pronounced because it marks the plural

So:

• prezzo ≈ PRET-tso
• prezzi ≈ PRET-tsee

The sentence follows a very common Italian structure:

Subject + verb + adjective

Here that gives:

• I due prezzi = subject
• sono = verb
• uguali = adjective

So the full structure is:

The two prices + are + equal/the same

This is a very useful model for many other Italian sentences.