En un rectángulo, cada ángulo es recto.

In a rectangle, each angle is right.

Breakdown of En un rectángulo, cada ángulo es recto.

• un: a
• ser: to be
• en: in
• cada: each

Questions & Answers about En un rectángulo, cada ángulo es recto.

Why does the sentence start with en?

Here en means something like in or within the figure.

So En un rectángulo means In a rectangle or In any rectangle.

In maths and geometry, Spanish often uses en this way:

• En un triángulo...
• En un círculo...
• En un cuadrado...

It introduces a general fact about that shape.

Why is it un rectángulo and not el rectángulo?

Un rectángulo is used because the sentence is talking about any rectangle, not one specific rectangle.

• En un rectángulo... = in a rectangle / in any rectangle
• En el rectángulo... = in the rectangle, meaning a specific rectangle already mentioned

So the indefinite article un gives a general, definition-like meaning.

Why is it cada ángulo and not cada ángulos?

Because cada is followed by a singular noun in Spanish.

So:

• cada ángulo = each angle / every angle
• not cada ángulos

More examples:

• cada día
• cada persona
• cada lado

This is different from English, where every also takes a singular noun: every angle.