Now, in ∆ABC,
there can be 3 cases
All angles are acute
One angle is right angle (90°)
One angle is greater than 90° (i.e one angle is obtuse)
If all angles are acute, it is an acute angled triangle.
If one angle is right angle, it is a right angled triangle.
If one angle is greater than 90°, it is an obtuse angled triangle.
(a) is an acute-angled triangle
(b) is a right-angled triangle
(c) is an obtuse angled triangle
(d) is a right angled triangle
(e) is an obtuse angled triangle
(f) is an acute angled triangle

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.