Base angles of an isosceles triangle Chapter 5 (p. 244)
The two angles adjacent to the base of an isosceles triangle
An isosceles triangle is a triangle with two sides of equal length. Since the two sides are equal, the two angles opposite those sides are also equal. These two angles are called the base angles of the isosceles triangle.
To find the measure of the base angles of an isosceles triangle, you can use the following formula:
Base angle = (180 degrees – vertex angle) / 2
The vertex angle is the angle formed by the two equal sides of the triangle. To find the vertex angle, you can use the following formula:
Vertex angle = 180 degrees – 2(base angle)
For example, if you know that the two equal sides of an isosceles triangle have a length of 8 cm each, and the vertex angle is 100 degrees, you can use the formula to find the base angles:
Base angle = (180 – 100) / 2 = 40 degrees
Then, you can use the formula to find the vertex angle:
Vertex angle = 180 – 2(40) = 100 degrees
So, the two base angles of the triangle are both 40 degrees, and the vertex angle is 100 degrees.
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