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# Angle calculated 135° instead of 136° Geogebra Classic 6

Kharlamov Konstantin shared this problem 5 years ago
Not a Problem

This does not seem to be a rounding error, because the actual angle is 136.028°, so if it get rounded, it would be in between 136..137. The correct angle can be quickly calculated e.g. with this online calculator https://www.triangle-calcul... (but I found the error for writing a test case for a function calculating an angle for my car bot).Steps to reproduce:

1. Press button "Create angle", and place it to points A=(1,0), B=(0,0), C=(-1,1), (as in illustration) (I had to place screenshot here https://imgur.com/a/O6FwH because site complains "path not found at" for images uploaded locally — I guess there's some silly timeout — deleting and reuploading the image doesn't help, and using a link doesn't do any better either).

Expected: the angle shown is 136°

Actual: the angle shows 135°

Additional info:

Geogebra version: 6.0.414.0-offline

OS: Archlinux.

## Comments (4)

1

The angle IS actually 135°.

Please note that line OC is the bisector of the 2nd and 4th quadrant of the plane.

1

Then why calculations using lengths consistently getting 136°?

1

Because you are probably entering in that site the approximate values for the length of sides instead of exact ones.

Use trig, or if you don't know it, use the Pythagoras theorem to obtain the exact values of the sides.

Exact means e.g. sqrt(2) instead of 1.41

1

I think the angle is 135 deg. I calculated it from vertex coordinates using the tool:

Sides are sqrt(2) and sqrt(5). If you round these sides to hundreds, you lose some precision and angles are different.

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