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why is a right angle 90 degrees

Why is a 90 degree angle called a 'right' angle, why not 'left' or 'wrong'? Because it is the correct angle required for many construction tasks - laying out buildings etc. Along similar lines there is a species of whale which is called the "Right Whale", simply because it was the right whale to hunt if you wanted to make maximum profits. Simon Blake's answer sounds a bit like a guess.


A right angle would be "wrong" for just as many tasks. Right, meaning "correct", and right, meaning "straight", do have the same root, but "right angle" derives from the second rather than the first. A right angle was described in ancient geometry as the meeting of two right, ie straight, lines, with regard to dimensional axes.
I was wondering why a 90 degree angle is called a Right angle.


I mean why isn't called a left angle. Hi Joseph, The term right in right angle comes from the meaning of right as proper, or in accordance to justice or equality. It comes from the way a right angle was originally defined. When two straight lines intersect they form two angles. When these angles are equal then this is a fair or just situation and the angles are "right".


Your question "Why isn't called a left angle? " may lead you to wonder if these two distinct meanings of right is an anomoly of English, but it is not. In most western european languages there is one word that means right as opposed to left, right as proper and also right as a human right.

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