[tex]\begin{gathered} \text{Use cosine rule,} \\ AC^2=AB^2+BC^2-2\times AB\times BC\times\cos B \\ (7.12)^2=(7.12)^2+(7.12)^2-2\times7.12\times7.12\times\cos B \\ \cos B=\frac{1}{2} \\ B=60^{\circ} \\ \end{gathered}[/tex]
You can also find the angle B by just seeing, because every sides are equal.
And it makes equilateral triangle.
And equilateral triangle has every angle as 60 Degree.
