Question

Which of the following information are needed to draw a unique $\Delta$ABC?

• A. Length of AB and AC only
• B. Length of AB, AC and BC
• C. ∠A, ∠B and ∠C
• D. AB, BC and ∠C

Answer 1

Answer: (B), (D)

The correct options are
B

Length of AB, AC and BC

D

AB, BC and ∠C

We need three measurements to construct a triangle. The lengths of sides AB, AC and BC are required to draw a unique $\Delta$ABC (SSS criterion). With the set of measurements of three angles, we can construct infinite triangles (AAA is not a congruence criterion). Similarly, two angles and excluded angle will not give a unique triangle (SSA is not a congruence criterion).