# Isosceles triangle theorem to evaluate the opposite angles:

**sosceles triangle theorem** states that the angles opposite to the equal sides are also equal. Many mathematicians have provided the **isosceles triangle proof**. This can also be practically proved by drawing a triangle with 2 equal sides. Now if you measure the opposite angles using a compass, you will notice that they are exact.

## Have a look at Isosceles triangle formula:

Now we know **what is an isosceles triangle**. It's time to study **isosceles triangle formula**. Consider the following diagram.

(1) Area of Isosceles triangle = bh/2

(2) Perimeter of Isosceles triangle = 2a + b

(3) Altitude of Isosceles triangle** **=** **√(a^{2} – b^{2}/4)

where a are the equal sides, b is the base and h is the **height of isosceles triangle**.

## Some Important Isosceles triangle properties:

** **The **isosceles triangle properties** helps to understand the **isosceles triangle** better. The **definition of isosceles triangle **itself is an important property. The **isosceles triangle definition **also provides another important property about the angles as discussed in above theorem. If the third angle is a right angle, than **triangle isosceles** is known as **isosceles right triangle **which makes the other two angles equal to 45°.

## What is an Acute Isosceles triangle?

** Isosceles triangle rules **states that an Isosceles triangle with all its angles less than 90° is known as **acute isosceles triangle**. The figure below makes this thing clear.

As shown in the diagram, the angles opposite to equal sides are also equal (shown with black lines). We can observe that all the angles are less than 90°.

## What is an Obtuse Isosceles triangle?

** **Isosceles triangle with one of its angle greater than 90° is known as **obtuse isosceles triangle**. The diagram shows that one of the angle marked red is greater than 90°.

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