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If you are dealing with an isosceles triangle, if one of the base angles measures 42 degrees then the other base angle measures 42 degrees. (By definitioin an isosceles triangle has at least 2 equal sides and the angle opposite those sides with be equal.) If you add up the degrees in each angle within a triangle, it will always equal 180 degrees. Knowing all this you can set up a formula: Angle 1 + Angle 2 + Angle 3 = 180 42 + 42 + Angle 3 = 180 Angle 3 = 96 degrees
In the diagram, ABC is an isoscels triangle with the congruent sides and , and is the median drawn to the base . We know that ∠A ≅ ∠C, because the base angles of an isosceles triangle are congruent; we also know that ≅ , by definition of an isosceles triangle. A median of a triangle is a line segment drawn from a vertex to the midpoint of the opposite side. That means ≅ . This proves that ΔABD ≅ ΔCBD. Since corresponding parts of congruent triangles are congruent, that means ∠ABD≅ ∠CBD. Since the median is the common side of these adjacent angles, in fact bisects the vertex angle of the isosceles triangle.
20 degrees
thank goodness for my math teacher, norm! he said only in an isosceles triangle. The bisector of the vertex angle of an isosceles triangle is perpendicular to the base! =)
The formula is: Area = base * height. With an isosceles triangle, two of the angles are congruent and their opposite sides are congruent. There is one remaining angle (that will be referred to as the top angle) and its opposite side (the base). You will probably have to drop a perpendicular line from the top angle to the base. This will bisect the base into two equal parts. Also, you now have two congruent right triangles. It depends on what you know with this triangle in order to find its height and/or base. However, use the Pythagorean Theorem and I'm sure you can work it out.