Question

What is the measure of a base angle of an isosceles triangle if the measure of the vertex tangle is 38 degrees and the two congruent sides each measure 21 units?

Answer 1

The measures of the angles of the isosceles triangle are 55, 55 and 70.

Explanation:

An isosceles triangle has two congruent base angles and a vertex angle.

Let b =the measure of one of the base angles.

Let v = the measure of the the vertex angle.

The vertex angle is 40 degrees less than the sum of the base angles.

v = b + b − 40 = 2 b − 40

The sum of the measures of the angles of a triangle is 180.

b + b + v = 180

Substitute 2 b − 40 for v .

b + b + 2 b − 40 = 180

4 b − 40 = 180

+40+40

Combine like terms.

Add 40 to both sides.

4b=220

Divide by 4

4 b/4 = 220 /4

b = 55

v = 2 b − 40

v = 2 ( 55 ) − 40 = 70