Isosceles Triangle - Angles
Date: 11/6/96 From: Michelle Subject: Geometry Given that one base angle of an isosceles triangle is 39 degrees, find the measure of the other two angles in the triangle.
Date: 11/07/96 at 12:46:30 From: Doctor Wilkinson Subject: Re: Geometry To start, let's make sure you understand the definitions of the terms. As isosceles triangle has two congruent sides with a third side that is the base. A base angle of an isosceles triangle is one of the angles formed by the base and another side. Base angles are equal because of the definition of an isosceles triangle. A picture would probably help here: A . / \ ABC = ACB = 39 degrees / \ BAC = ?? / \ / \ / \ / \ / \ ._______________. B C base ABC is the isosceles triangle. AB is congruent to AC. Angle ABC is congruent to angle ACB. These are the base angles. Now let's look at what we're given and what we're asked to find out. We're given that one of the base angles is 39 degrees. We know that the base angles are congruent, so we actually know both base angles are 39 degrees: that is, we know that angle ABC and angle ACB are both 39 degrees. We're asked to find out the measures of the other two angles, and we've already got one of them, so all we need to find out is the measure of angle BAC. We know two out of the three angles, but we've used up the specific information we were given. Now we need to look for some general rule that will connect the unknown (the angle BAC) to the known (the angles ABC and ACB). Do you know such a rule? Now it's your turn. If you're still stuck, let me know. -Doctor Wilkinson, The Math Forum Check out our web site! http://mathforum.org/dr.math/
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