Jessica is making a repeating pattern following the rule “triangle square circle what will be the 50th shape in the pattern?

Triangle, then a square, so the pattern is more or less ▲ ■ ▼ ■ ▲ ■ ▼ ■ ▲ ■ ▼ ■  and so on.

notice, the first is the triangle, the second is the square, so all ODD integers, 1,3 5, 7 and so on, will be triangles.

and all EVEN integers will be squares, so, the 50th shape is, well, you already know.