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# Geometry/Angles

Question
Can you recommend an online angle calculator for determining the needed lengths of three lines to create a certain angle among them? The ones I saw from a basic google search seemed like they were asking for more information than I have.

I know of no calculator to do this, but what I can say is that the size of angles in a triangle add to 180°.  This means if you know angle A and B, angle is found as 180° - A - B.

If we have a right triangle (one angle is 90° and the other two are acute), the sum of the two smaller angles is 90°.

If we have angle A, and are given that angle B is twice A and that angle C is
three times the measure of A, then we have 2A + A + 3A = 180°.
This gives A = 30°, so the other angle is 2 times this, which is 120°.

I believe the best way to do this is use Excel.
To do the calculations in Excel needs the angle be to 180°.

If the angles are measured in radians, the sum of the three angles of a triangle is pi.

The correct formulas to use is given any triangle with sides a and b with an angle between them C,
then a² + b² - 2ab*cos(C)= C².

Geometry

Volunteer

#### Scott A Wilson

##### Expertise

I can answer whatever questions you ask except how to trisect an angle. The ones I can answer include constructing parallel lines, dividing a line into n sections, bisecting an angle, splitting an angle in half, and almost anything else that is done in geometry.

##### Experience

I have been assisting people in Geometry since the 80's.

Education/Credentials
I have an MS at Oregon State and a BS at Oregon State, both with honors.

Awards and Honors
I was the outstanding student in high school in the area of geometry and math in general.

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Over 8,500 people, mostly in math, with almost 450 in geometry.