![]() ![]() The angles opposing the triangle's two equal sides are always equal.As the two sides of this triangle are equal, the uneven side is referred to as the triangle's base.Hence, the measure of the other two angles of an isosceles triangle is 55°. If we are given the measure of an unequal angle, we can simply calculate the other two angles using the angle sum property.Įxample: Let the measure of the unequal angle is 70° and the other two equal angles measures x, then as per angle sum rule, As a result, one of the angles is unbalanced. Two of the isosceles triangle's three angles are equal in measure, which is the polar opposite of the equal sides. As a result, we may employ Pythagoras theorem, which states that the square of the hypotenuse equals the sum of the squares of the base and perpendicular. The hypotenuse is the third unequal side of the triangle. Parts of a triangle Isosceles right triangleĪ right isosceles triangle has two equal sides, one of which serves as the perpendicular and the other as the triangle's base. If the two angles opposing the legs are equal and smaller than 90 degrees, the isosceles triangle is called an acute isosceles triangle. The isosceles triangle is classed as acute, right, or obtuse depending on the angle between the two legs. The perpendicular bisector of the base of every isosceles triangle has a symmetry axis. Legs, base, and height are the three dimensions of a triangle, as we all know. Types of Isosceles Triangle Isosceles acute triangle The apothem of a regular polygon is also the height of an isosceles triangle formed by the center and a side of the polygon, as shown in the figure below.įor the regular pentagon ABCDE above, the height of isosceles triangle BCG is an apothem of the polygon.In general, the isosceles triangle may be divided into three types: The length of the base, called the hypotenuse of the triangle, is times the length of its leg. When the base angles of an isosceles triangle are 45°, the triangle is a special triangle called a 45°-45°-90° triangle. Base BC reflects onto itself when reflecting across the altitude. Leg AB reflects across altitude AD to leg AC. The altitude of an isosceles triangle is also a line of symmetry. So, ∠B≅∠C, since corresponding parts of congruent triangles are also congruent. Based on this, △ADB≅△ADC by the Side-Side-Side theorem for congruent triangles since BD ≅CD, AB ≅ AC, and AD ≅AD. Using the Pythagorean Theorem where l is the length of the legs. ABC can be divided into two congruent triangles by drawing line segment AD, which is also the height of triangle ABC. ![]() Refer to triangle ABC below.ĪB ≅AC so triangle ABC is isosceles. The base angles of an isosceles triangle are the same in measure. Using the Pythagorean Theorem, we can find that the base, legs, and height of an isosceles triangle have the following relationships: The height of an isosceles triangle is the perpendicular line segment drawn from base of the triangle to the opposing vertex. The angle opposite the base is called the vertex angle, and the angles opposite the legs are called base angles. Parts of an isosceles triangleįor an isosceles triangle with only two congruent sides, the congruent sides are called legs. DE≅DF≅EF, so △DEF is both an isosceles and an equilateral triangle. ![]()
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