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## Main Question or Discussion Point

for arbitrary quadrangle, if we know four side and one diagonal, can we know another diagonal? how?

- Thread starter enricfemi
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for arbitrary quadrangle, if we know four side and one diagonal, can we know another diagonal? how?

tiny-tim

Science Advisor

Homework Helper

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Do you know the formulas for sides-and-angles of a triangle?

If so, you have two triangles, ACB and ACD, say, so you can find all the angles.

In particular, you can find angles CAB and CAD.

Add them to get angle DAB.

Now you have a triangle DAB of which you know two sides and the angle in between.

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THX:rofl:

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