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.
The third angle of an isosceles triangle doesn't have a name.
Vertex angle
The base
The base angles of an isosceles triangle are congruent. The vertex angle of an isosceles triangle is not necessarily congruent to the base angles.
They're the 'base angles'.
-- An isosceles triangle has two equal sides. -- An isosceles triangle has two equal angles. -- An isosceles triangle has two equal interior-angle bisectors. -- The bisector of the vertex angle of an isosceles triangle is also the perpendicular bisector of the triangle's base.
In general, they are not. In an isosceles triangle, the perpendicular bisector of the base is the same as the bisector of the angle opposite the base. But the other two perp bisectors are not the same as the angle bisectors. Only in an equilateral triangle is each perp bisector the same as the angle bisector of the angle opposite.
No. It need not be the base angles that are equal, it can be one of the base angles and the top angle (if the triangle is tipped over). Also, the base angle are equal in an equilateral triangle - although an equilateral triangle is a special kind of isosceles triangle.
If you mean the vertex where the two equal sides of an isosceles triangle intersect, the side is the base.
The two "base" angles.
An isosceles triangle has three interior angles whose base angles are equal.
For an isosceles triangle with vertex 46 degrees, the sum of the remaining two base angles is 180-46 = 134 degrees. Base angles are equal because it's isosceles, so each angle is half of their sum. 134/2 = 67 degrees. Thus, any isosceles trapezoid formed inside that isosceles triangle by drawing parallel lines to the triangle's base, will have base angle measures of 67 degrees, which are triangle's base angles.