Wendy described four triangles as shown below:

triangle a: all sides have length 9 cm.

triangle b: two sides have length 10 cm, and the included angle measures 60°.

triangle c: two angles measure 50°.

triangle d: base has length 8 cm, and base angles measure 45°.

which triangle is not a unique triangle?

The Triangle thats not unique is letter D

Triangle C is not unique
A - all sides 9cm, equilateral
B - 2 sides measure 10cm and included angle 60°, it is an equilateral triangle
C- two angles 50°, opposite sides equal, isosceles triangle, it can have variable length of sides.
D - base 8cm, base ANGLES 45°, it's an isosceles triangle but with a fixed lengh of other two sides.