Answer: C. 84°
Explanation:
From the given figure , in ΔABD and ΔBCD
∠A=∠C=90°
AD=CD [given]
BD=BD [Reflexive property]
Therefore, ΔABD ≅ ΔBCD by RHS congruence theorem
⇒∠CBD≅∠DBA=42°......................[By CPCTC]
Now, ∠ABC=∠CBD+∠DBA
⇒∠ABC=42°+42°=84°
- RHS congruence theorem says two right triangles are congruent if the hypotenuse and one side of one triangle are equal to the hypotenuse and the corresponding side of the other triangle.