How are the sides and angles of a triangle related?

There are many types of connections. First, it all depends on the shape, the angles in which are considered. If this is a right-angled triangle, then in the seventh grade these are signs of equality in the hypotenuse and legs, and the 9th grade is already the formulas for finding sines, cosines, tangents, cotangents of angles, using the figure itself. If we take the same isosceles one, then due to the equality of the sides, the angles at the base are equal. And in an equilateral triangle, due to the equality of the sides, all the angles are generally equal.