Name the triangles: a) d) In RST, RS = ST = TR. If RS = 9 cm, find the perimeter. b) LMN is an isosceles triangle. LM = 6 cm and MN = 4 cm. What is the length of NL? The perimeter of ABC is 17 cm. What is the length of CA?

The angles given are $90^\circ$, $60^\circ$, and $30^\circ$. Since one angle is exactly $90^\circ$, this is a right-angled triangle.

The angles given are $100^\circ$, $45^\circ$, and $35^\circ$. Since one angle ($100^\circ$) is greater than $90^\circ$, this is an obtuse-angled triangle.

The angles given are $80^\circ$, $60^\circ$, and $40^\circ$. Since all angles are less than $90^\circ$, this is an acute-angled triangle.

a) The triangle is a right-angled triangle.

b) The triangle is an obtuse-angled triangle.

c) The triangle is an acute-angled triangle.