Informal: one angle that matches the corner of a (rectangular) piece of paper, or the angle at the base of a funding L or the height of a resources T.

You are watching: Why is a right angle called a right angle

These room all instances of right angles: 


These space not appropriate angles:

The 2 at the left are both obtuse (“wider” than a ideal angle) and also the 2 at the appropriate are both acute (“sharper” 보다 a right angle).

Mathematical background

Constructing a appropriate angle

You deserve to construct a best angle simply by urgent paper, even one that has been ripped so the there are no directly edges!


In any direction, wrinkles the piece of paper. For example:


The an outcome will look like this:


Then do a second fold, being careful that the original crease lies on top of itself.


The an outcome will look prefer this:


When friend unfold the item of paper, the two creases will be perpendicular to each other. The four angles space all appropriate angles.


Why does this work? The very first fold creates a straight-line crease. The 2nd fold crease one component of the line top top the other. If an angle is folded v its peak so that one side of the edge lies directly on the other, the fold bisects the angle. The right line of the initial crease develops a straight angle (180°) approximately any allude on it. Folding with that suggest bisects the angle, so the result angles room each 90°, and so they are appropriate angles.

Facts around right angles

Four best angles fit about a point. The method we specify degrees, a “full turn” around a suggest is 360°, so the measure of each right angle is one 4th of that: 90°. In informal speech (not mathematics), right-angle corners room sometimes referred to as square corners even though, as in the forms above, there is nothing “square” around the shape. 2 lines that room at ideal angles come each various other are stated to be perpendicular to every other.

Related math ideas

perpendicular, angle, rectangle

“Right”: What’s in a word?

The gh in “right” was once pronounced; it descended from the c in Latin “rect-.” In English, words with “rect-” in them frequently have meanings related come “right.”

The word right has countless meanings. Among its interpretations is ‘correct,’ opposing of ‘wrong.’ (When we acquire something wrong, we try to rectify ours error.) Another an interpretation is the contrary of ‘left.’ quiet another definition is ‘straight’ or ‘directly,’ as in “After school, please come appropriate home.”

Why all those meanings? What execute they all have in common?

Like many words, right has great-…-great grandparents. The more quickly ancestor we know can have sound something choose reg, and also many the right’s cousins room spelled favor reg or rect. The original definition was something favor ‘to move in a directly line.’ when we regulate something, us are maintaining it top top track, keeping it from changing, keeping control. Rules and also regulations keep civilization ‘following the right path,’ law the ideal thing. The word ruler is a cousin that regular and so it is a cousin of right. Once the g in a native like consistent is quiet (as the is in right, and many other words), we acquire ruler. A leader helps you draw a directly line. A king is a ruler, who provides rules that control the country. Tyrannosaurus Rex to be ‘king’ of the dinosaurs; ‘rex’ is the Latin word for king, and is pertained to reg and also rect. The king—royal is simply regal with another silent g—was the richest, most an effective person, that gave human being their rights, or took them away! as soon as we name youngsters Richard or Regina or, of course, Rex—or Henry or Roy v yet an additional silent g—we room comparing them to kings and also queens!

If right method something favor ‘straight,’ why execute we say best turn?

The word right suggests strength — not just the king but the ideal hand — and so a turn to the appropriate is a rotate toward that right hand.

Where go a best angle acquire its name? space there “left angles,” too?

No, the appropriate angle has nothing to perform with best or left turns.

See more: Parathyroid Hormone Positive Or Negative Feedback, Negative Feedback

In this map, us say the Walnut Street provides a best angle with main Street due to the fact that it goes as ‘straight’ far from key Street together possible. Corn Street veers turn off at a various angle.