Using cosine rule
[tex]\begin{gathered} \cos A=\frac{b^2+c^2-a^2}{2\times b\times c} \\ \text{ =}\frac{30^2+30^2-20^2}{2\times30\times30}\text{ = }\frac{900\text{ + 900 - 400}}{1800}=\frac{1400}{1800} \\ \text{ = 0.7777} \\ A\text{ = }\cos ^{-1}0.7777=38.9^0\approx40^0 \end{gathered}[/tex]Since two sides of the triangles are equal, then the triangle is an issoseles triangle
In an issoseles triangle, two base angles are equal
This implies, angle at B = angle at C = x
Sum of angles in a triangle = 180 degrees
[tex]\begin{gathered} \text{then } \\ x+x+40^0=180^0 \\ 2x=180^0-40^0 \\ 2x=140^0 \\ x\text{ =}\frac{140^0}{2}=70^0 \end{gathered}[/tex]angle A = 40 degrees , angle B = 70 degrees , angle C = 70 degrees
The triangle is SAS , two sides are equal with an included angle
SSS is for triangles with equal sides
