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Because, thanks to Pythagoras, the three sides are linked by an equation. Thus the measure of the third side can always be derived from the knowledge of the other two.

Q: Why can you use any two sides of a right angle to find the third side?

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Depends on the Triangle. Right triangles with a 90 degree angle: http://en.wikipedia.org/wiki/Pythagorean_theorem

You need either two sides given, to find a third side. Or > you need one side and an angle, to find another side.

The cosine rule which is: a2 = b2+c2-2*b*c*cosine A This is used to find the third side of a triangle when the two other sides are known along with the angle between them. Used when the triangle is not a right angle.

If 2 sides are known then use Pythagoras' theorem to find the 3rd side of a right angle triangle.

If two sides of a triangle with a right angle are known, the Pythagorean Theorem can help you find the third one. It can also be used to verify whether a certain triangle is, indeed, a right triangle (if the three sides are known).

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Depends on the Triangle. Right triangles with a 90 degree angle: http://en.wikipedia.org/wiki/Pythagorean_theorem

You use the law of Pythagoras: a2 + b2 = c2, where a and be are the sides adjacent to the right angle, and c is the side opposite. Replace the two sides that you know, and solve for the third one. Pythagoras: hypotenuse squared = sum of squares of other two sides. If you know two of the sides you can calculate the third as above.

You need either two sides given, to find a third side. Or > you need one side and an angle, to find another side.

They are used to find the angle or side measurement of a right triangle. For example, if 2 sides of a right triangle have known values and an angle has a known measurement, you can find the third side by using sine, cosine or tangent.

The cosine rule which is: a2 = b2+c2-2*b*c*cosine A This is used to find the third side of a triangle when the two other sides are known along with the angle between them. Used when the triangle is not a right angle.

If 2 sides are known then use Pythagoras' theorem to find the 3rd side of a right angle triangle.

If two sides of a triangle with a right angle are known, the Pythagorean Theorem can help you find the third one. It can also be used to verify whether a certain triangle is, indeed, a right triangle (if the three sides are known).

add all of the sides together

A right angle, by definition, is 90 degrees. If you mean what are the other angles in a right triangle, you need one of the other angles in the triangle or the length of one side (not the hypotenuse) any two sides. You can then find the third side by Pythagoras, then the other two angles by simple trigonometry.

It is a right angle triangle and its largest angle is 90 degrees

Find the total length of two adjoining sides (two sides which form a right angle) and multiply by two.

If you know the lengths of two sides then use Pythagoras' theorem to find the third side.