To determine what type of triangles we have we can use the following rules:
• If the sum of the squares of the smaller lenghts are more than the square of the bigger length then the triangle is acute.
,
• If the sum of the squares of the smaller lenghts are equal than the square of the bigger length then the triangle is a right one.
,
• If the sum of the squares of the smaller lenghts are less than the square of the bigger length then the triangle is obtuse.
With this in mind.
First triangle:
then the first triangle is acute
Second triangle:
then the second triangle is obtuse.
Third triangle:
then this is a right triangle.
Fourth triangle:
then this triangle is acute.