Consider the triangle ABC.
In triangle ABC, side AB is equal to AC means that angle B is equal to angle C.
Determine the value of angle in triangle ABC.
[tex]\begin{gathered} \angle A+\angle B+\angle C=180^{\circ} \\ x^{\circ}+50^{\circ}+50^{\circ}=180^{\circ} \\ x^{\circ}=80^{\circ} \end{gathered}[/tex]
Consider the triangle BCD.
In triangle BCD, side BD is equal to side CD, so angle B is equal to angle C.
Determine the angle of triangle BCD.
[tex]\begin{gathered} \angle B+\angle C+\angle D=180^{\circ} \\ y^{\circ}+y^{\circ}+120^{\circ}=180^{\circ} \\ y^{\circ}=\frac{60^{\circ}}{2} \\ =30^{\circ} \end{gathered}[/tex]
So correction answer is D part.
