A triangle whose **one of the angle is Obtuse angle** is known as **Obtuse Triangle**

**But what is Obtuse Angle?**

Angle whose measurement is above 90 degree but below 180 degree

Hence Obtuse triangle has one angle between 90 to 180 degree

**Examples of Obtuse Triangle**

Given below are two examples of Obtuse triangle

⟹ Note one of the angles is between 90 and 180 degree

⟹ Also, sum of all angles in triangle = 180

**Obtuse Triangle Property**

**(1) In Obtuse Triangle, one angle is obtuse and other two angles are acute angles**

**(02) A triangle cannot have more than one obtuse angle**

If x, y and z are the three angles of triangle.

Angle property of triangle says: Sum of all three angle = 180 degree

i.e. x + y + z = 180

If two angles are obtuse angle ( x & y = 91 degree)

91 + 91 + z will be greater than 180 degree.

The angle property will not be satisfied.

Hence, there can be only one Obtuse angle in the triangle

**(03) The side opposite to obtuse angle is the longest side**

In the above example, note angle B is an obtuse angle (also the largest one)

So, the side opposite to the largest angle is the longest

Hence AC is the longest side of triangle ABC

**(04) Circumcenter of Obtuse Triangle**

The circumcenter of obtuse triangle **lies outside the triangle**

**What is Circumcenter?**

It is the center of circle which crosses all the vertex of triangle

Is is located at the intersection of perpendicular bisector of triangle

**Locating Circumcenter of Obtuse triangle**

**Step 01**

draw perpendicular bisector of side BC

**Step 02**

Now draw perpendicular bisector of side AC

Point O is the point of intersection of two perpendicular bisector, hence circumcenter of triangle ABC

From the above diagram we concluded that:

(a) In obtuse triangle, the circumcenter is located outside the triangle

(b) The circumcenter is located towards the longest side of the triangle

**(05) Centroid of Obtuse Triangle**

The centroid of obtuse triangle **lies inside the triangle**

Infact, the centroid of any triangle lies inside the body

**But what is centroid?**

Centroid is the central point of the geometrical figure.

It is also the center of mass of any object, where the entire mass is concentrated.

It is located at the intersection of median.

Locating centroid of Obtuse triangle

**Step 01**

Find the midpoint of side AB of triangle and join it with the opposite vertex

**Step 02**

Similarly find the midpoint of side BC and join it with opposite vertex

The point O is the intersection of two medians and is the centroid of the triangle

**Conclusion**

The centroid of obtuse triangle lies inside the body

**Area of Obtuse Triangle**

There are two formulas for calculating area

(a) Formula when base and height lengths are given

(b) Formula when length of all sides are given

**Formula when Base and Height lengths are given **

Given is the obtuse triangle ABC with following information:

⟹ length of base is b cm

⟹ perpendicular distance of base and opposite vertex is h cm

Note that we have to extend the triangle (as shown in dotted line) to find the perpendicular height (h cm )

If above information is provided then use the following formula

Area=\ \frac{1}{2} \times \ base\ \times height**Formula when side lengths are given**

Given below is the obtuse triangle with sides a, b and c cm

Follow the below step to calculate the triangle area

**Step 01**

Calculate semi perimeter of triangle

S\ =\ \frac{a+b+c}{2}

**Step 02**

Now use the area formula

Area\ =\sqrt{S\ ( S-a)( S-b)( S-c)}

**Frequently Asked Question : Obtuse Triangle**

**(01) Check if the below triangle is Obtuse Triangle**

This is not an obtuse angle.

In Obtuse angle, the angle measurement should be above 90 degree

(02) What is the location of circumcenter, centroid and orthocenter of Obtuse Triangle?

Read Solution

Circumcenter : Outside the triangle

Centroid : Inside the triangle

Orthocenter : Outside the triangle

(03) Can we apply Pythagoras theorem to Obtuse triangle

Read SolutionNO!!!

Pythagoras Theorem only applied to right triangle

(04) How to know if the triangle is Obtuse Triangle?

Read SolutionThere are two methods to find out

(a) Check Angles

If any of the angle measurement is above 90 degree then the triangle is Obtuse

(b) Check Side Lengths

If the sides follows following rule, then it is obtuse angle

c^{2} >\ \ a^{2} +b^{2}

Where, c is the longest side of the triangle