Acute angled triangle
A triangle is a two-dimensional geometrical shape having three sides and three angles. Based on the length of sides and the measure of interior angles, a triangle is categorized into three categories namely,
- Based on the length of sides
- Equilateral triangle: A triangle having all its sides of equal length is termed as an equilateral triangle. Each of the interior angles of equilateral triangle are equal and of the measure 60°.
- Isosceles triangle: A triangle that contains two of its sides with equal length and two angles equal is termed an isosceles triangle. The angles corresponding to the equal sides are equal.
- Scalene triangle: A triangle with all its sides of different length is termed as a scalene triangle. The angles corresponding to each side are of different measure.
- Based on the measure of angle
- Right triangle or right-angled triangle: A triangle which has one of its angles measuring 90° is called as a right-angled triangle. The other two angles are acute angles i.e. less than 90°.
- Acute angled triangle: A triangle having all its angles measuring less than 90° is called an acute angled triangle.
- Obtuse angled triangle: a triangle which has one of its angles measuring more than 90° is called an obtuse angled triangle. The other two angles are less than 90°.
Acute angled triangle
An acute angled triangle is the one which has all its interior angles less than 90° i.e. all the three angles of an acute angled triangle are acute. For example,
In any traingle ABC, ∠ABC = 40°
∠ACB = 75°
∠CAB = 65°
Here, all the angles of the given triangle are less than 90o. Therefore, ABC is an acute angled triangle.
Properties of acute angled triangle
- The measure of all the interior angles is less than 90°.
- The angle opposite to the largest side is the largest angle and the converse is also true.
- The angle opposite to the smallest side is the smallest and the converse is also true.
- The square of the largest side is equal to the sum of the square of the other two sides. Mathematically,
c² = a² + b²
where c is the largest side and a and b are the smallest.
- An equilateral triangle is a type of acute-angled triangle.
- Unlike an obtuse triangle, the orthocenter and circumcenter of an acute triangle are present in the interior of the triangle.
Perimeter of an acute-angled triangle
The perimeter of an acute-angled triangle is obtained by calculating the sum of its sides. For an acute triangle, let the measure of its sides be ‘a’ units, b units and c units then,
perimeter = a + b + c
Area of an acute-angled triangle
The area of an acute triangle can be calculated by two methods.
Method 1: By using the area of a triangle
We know that the area of a triangle in a two-dimensional plane is
Area = ½ . base. height
For a triangle of base b and height h
Area = ½ . b. h
Method 2: By using Heron’s formula
By Heron’s formula, we have known,
Area = √[s . (s-a) . (s-b) . (s-c)]
Where ‘s’ is semi perimeter calculated as
S = (a + b + c)/2