Posted by **Laura** on Monday, June 22, 2009 at 2:43pm.

how can we prove that an exterior angle of a triangle has measure equal to the sum of the measures of the 2 interior angles remote from it

- geometry -
**Reiny**, Monday, June 22, 2009 at 3:27pm
in triangle ABC extend BC to form the exterior angle at C, call that x

We know angle A + Angle B + angle C = 180

But angle C + x = 180, (by supplementary angle theorem)

so angle A + angle B + angle C = x + angle C

subtract angle C from both sides

angle A + angle B = x, the exterior angle

Therefore, the exterior angle of a triangle has measure equal to the sum of the measures of the 2 interior angles remote from it

- geometry -
**popopo**, Tuesday, September 1, 2009 at 7:39pm
rocks 12

## Answer this Question

## Related Questions

- Geometry - If the measure of an exterior angle of a triangle is 75 degrees, then...
- Geometry - The measure of an exterior angle of a triangle is 120. the interior ...
- math - One interior angle of a triangle has a measure that is equal to the sum ...
- geometry - The sum of the measures of two exterior angles of a triangle is 264o...
- math - Find the measure of the interior angle in a regular polygon if the ratio ...
- GEOMETRY - The sum of the measures of two exterior angles of a triangle is 264o...
- Geometry - What is the sum of the measures of the interior angles of a convex ...
- geometry - If the sum of the measures of the interior angles of a convex n-gon ...
- Geometry - 1. How many sides does a regular polygon have if one exterior angle ...
- College Math - In a certain triangle the measure of one angle is triple the ...

More Related Questions