The triangle is an isoceles triangle because
[tex]\begin{gathered} AB=AC \\ Therefore, \\ m\angle B=m\angle C \\ m\angle B=x+20 \\ m\angle C=x+20 \\ 180\text{ = m}\angle A+m\angle B+m\angle C \\ 180=3x+x+20+x+20 \\ 180=4x+40 \\ 180-40\text{ = 4x} \\ 140=4x \\ x=\frac{140}{4} \\ x=35 \end{gathered}[/tex]
